20.5 M - Thierry Karsenti
Transcription
20.5 M - Thierry Karsenti
COMPULSORY 1 READINGS 1 According to the author of the module, the compulsory readings do not infringe known copyright. 11. COMPULSORY READINGS An illustration of a fruit fly Drosophila melanogaster (SEM X60) taken from http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgeninteract.htm where permission was given by Dennis Kunkel at www.DennisKunkel.com to use the image in the former website. The following copyright regulations to Cell Biology by Dalton, et al. apply: You may copy and distribute the document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. Reading 1: Complete reference: The structure and function of Prokaryotic and Eukaryotic cells. 1. The Study Guide to the Science of Botany that is used in this section of the work is a textbook at Wikibooks shelved under Biology and intended to establish a course of study in the subject of Botany, utilizing articles provided in Wikipedia(http://www.Wikipedia.org/), with links to other relevant web sites and other Wikibooks as appropriate. In some cases, portions of the text from Wikipedia articles have been used to materially develop introductory text within 2. Cell Biology, Mark Dalton and others http://en.wikibooks.org/wiki/Cell_biology of which 30 pages covering cell structure and function have to be read prior to working through the learning activities to follow. the Guide. Focus your attention mainly to Chapter 2 of the Study Guide as it applies to the structure and function of ells only. 3. Prokaryotes: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookglossPQ.html 4. Cellular organisation: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL2.html Abstract: The introductory section address the differentiation of cells with specific reference to cell structure and its relationship to cell division (mitosis and meiosis) and the transfer of genetic material. Rationale: The main aim with the readings is to allow you to come to terms with the structures of prokaryotic and eukaryotic cells and also to relate the structure of the cells to function with specific reference to mitosis, meiosis and the transfer of genetic material. Reading 2: Mitochondrion - From Wikipedia, the free encyclopaedia Complete reference: http://en.wikipedia.org/wiki/Mitochondria (Downloaded 28th August 2006) Abstract: The chapter commences describing the structure of a mitochondrion, followed by energy conversion and the release of great amounts of heat. The chapter also links to a later section of the work where the task of the mitochondrion in terms of genetic transfer and population genetic studies will be highlighted. What the chapter also traces is to explain how mitochondrial inheritance occurs and what influence this could have on future generations. Rationale: The main purpose with this section of the work is to give you the opportunity in working through an on-line text with the main intention of acquainting yourself with the basic structure and function of mitochondria. The text is vividly illustrated containing a variety of on-line links that will give you access to the discussion and description of all the minute details relating to cell mitochondria. Reading 3: Cell organelles Complete reference: http://en.wikipedia.org/wiki/organelles (Downloaded 28th August 2006) Abstract: The following description applies specifically to the second ‘Wikipedia’ references listed as URL in this section. It mentions the fact that eukaryotes are the most structurally complex known cell type, and by definition are in part organized by smaller interior compartments, that are themselves enclosed by lipid membranes that resemble the outer most cell wall. The larger organelles, such as the nucleus and vacuoles, are easily visible with moderate magnification (although sometimes a clear view requires the application of chemicals that selectively stain parts of the cells); they were among the first biological discoveries made after the invention of the microscope. The article continues to explain that not all eukaryotic cells have all of the organelles listed and occasionally, exceptional species of cells are missing organelles that might otherwise be considered universal to eukaryotic cells (such as mitochondria). There are also occasional exceptions to the number of membranes surrounding organelles. Rationale: We have included this article to your reading resources as it could be regarded as a very comprehensive reader illustrating and explaining the structures and function of the majority of organelles contained in prokaryotic and eukaryotic cells. The different organelles are thoroughly compared with vivid and very clear descriptions relating to structure and function. It is once again a very good text to work through and to be reminded of the major differences of prokaryotic and eukaryotic cells. Reading 4: Cell Membranes Tutorial (*optional) Complete reference: http://www.biology.arizona.edu/cell_bio/problem_sets/membranes/index.html Abstract: As explained in the above-mentioned website “this exercise introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes. You should learn that membranes are fluid, with components that move, change, and perform vital physiological roles as they allow cells to communicate with each other and their environment. We also show that membranes also are important for regulating ion and molecular traffic flow between cells and that defects in membrane components, lead to many significant diseases.” The website suggests that you follow the following instructions: “The following problems have multiple choice answers. Correct answers are reinforced with a brief explanation. Incorrect answers are linked to tutorials to help solve the problem.” Rationale: The completion of a simple hands-on assessment activity will assist you in mastering the cell membranes more effectively. Reading 5: Cell nucleus Complete reference: http://en.wikipedia.org/wiki/Cell_nucleus Abstract: The following paragraph was taken from the following website: http://en.wikipedia.org/wiki/Cell_nucleus. “The article illustrates that in cell biology the nucleus is found in all eukaryotic cells and contains the nuclear genes that form most of the cell's genetic material. The section explains that nuclei have two primary functions namely to control chemical reactions within the cytoplasm and also to store information needed for cellular division. Aside from containing the cell's genome, the nucleus contains certain proteins whose interplay is thought to regulate the expression of genes. Gene expression at the nuclear level involves complex processes of transcription, pre-mRNA processing and the export of the mature mRNA to the cytoplasm.” Rationale: The section will provide you with a very thorough briefing on the structure of the components of the cell nucleus in the first place, but will also highlight the different functions of the nucleus as it applies to cell metabolism and genetics. Reading 6: Introduction to genetics 1. Complete reference: Genetics/Introduction From Wikibooks, the open-content textbooks collection "http://en.wikibooks.org/wiki/Genetics/Introduction" 2. Online Biology Book http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenintro.html Abstract: The short article illustrates that genetics is the study of the function and behaviour of genes and that offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the colour of a flower’s petals, the markings on a butterfly’s wings, or such human behavioural traits as personality or musical talent. Geneticists also seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. They also look hw tiny variations in genes can disrupt an organism’s development or cause disease. The article also explains how modern genetics involves genetic engineering, a technique used by scientists to manipulate genes. Rationale: Understanding the rationale behind genetics as field of study, will help us to come to terms with the changes often experienced in genetic material, the loci where these changes are actually taking place as well as the mechanism behind the transfer of fixed characteristics from one generation to the other. The examples provided in these introductory learning activities should prepare you to comprehend the more advanced descriptions and activities to follow. Reading 7: Fundamental understanding of Mendel’s law of dominance 1. Complete reference: Genetics/Mendelian Inheritance From Wikibooks, the open-content textbooks collection http://en.wikibooks.org/w/index.php?title=Genetics/Mendelian_Inheritence&action= edit§ion=1 2. Online Biology Book http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC Abstract: The short article explains that Mendel's first step in the many experiments he conducted was breeding pure breeding strains of peas. The traits (traits = characteristics) he studied included pea colour, height and whether the peas were wrinkled or smooth. Mendel crossed the pure breeding Parental Generation (designated P). He found that the first generation (F1) was exclusively phenotypically (phenotype = externally visible characteristic such as pea colour) one of the parental types. Mendel then crossed his F1 generation with itself. He found that the F2 generation showed a surprising trait, three quarters were like the F1 generation, while the remaining quarter were like the other Parents. From this Mendel realised that there were two versions of each loci, one of which expressed dominance over the other. He called this bi-particulate (bi = two) Inheritance. If a gene was following this 3:1 pattern it was said to be segregating normally. Rationale: The purpose of allowing you to work through this introductory passage on inheritance (with specific reference to the P1 and F2 generations) is to illustrate to you how the simple crossing of two individuals containing pure traits such as a pure breeding characteristic for shortness and a pure breeding characteristic for tallness would produce offspring reflecting only one of these characteristics in the first generation, called the F1 generation. The examples contained in the text are very clear and self-explanatory. Reading 8: Mitosis Complete reference: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html and Abstract: The second website (consulted 5 October 2006) listed above under (2) explains the reading of this specific article as follows: “Despite differences between prokaryotes and eukaryotes, there are several common features in their cell division processes. Replication of the DNA must occur. Segregation of the "original" and its "replica" follow. Cytokinesis ends the cell division process. Whether the cell was eukaryotic or prokaryotic, these basic events must occur.” Rationale: The article has been selected as a very basic comparative study between binary fission and mitoses. The article explains the two processes very carefully and with simple examples. The article has been selected as introductory passage for the other processes (meiosis) and activities to follow). Reading 9: Meiosis Complete reference: (1) http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeiosis.html (2) http://en.wikipedia.org/wiki/meiosis Abstract: The Wikipedia website (consulted 27 September 2006) listed above summarises meiosis as follows: “Meiosis is the process that transforms one diploid cell into four haploid cells in eukaryotes in order to redistribute the diploid cell's genome. Meiosis forms the basis of sexual reproduction and can only occur in eukaryotes. In meiosis, the diploid cell's genome, which is composed of ordered structures of coiled DNA called chromosomes, is replicated once and separated twice, producing four sets of haploid cells each containing half of the original cell's chromosomes. These resultant haploid cells will fertilize with other haploid cells of the opposite gender to form a diploid cell again. The cyclical process of separation by meiosis and genetic recombination through fertilization is called the life cycle. The result is that the offspring produced during germination after meiosis will have a slightly different blueprint which has instructions for the cells to work, contained in the DNA. This allows sexual reproduction to occur.” Rationale: Understanding meiosis will assist you in coming to a better understanding of genetic transfer and of the role chromosomes play during the transfer of characteristics. Reading 10: Genetic manipulation – terminator, Terminator Technology, and Genetically modified organisms Complete reference: http://en.wikipedia.org/wiki/Terminator_(genetics) http://en.wikipedia.org/wiki/Terminator_Technology http://en.wikipedia.org/wiki/Genetically_modified_organism Abstract: A genetically modified organism (GMO) is an organism whose genetic material has been altered using techniques in genetics generally known as recombinant DNA technology. Recombinant DNA technology is the ability to combine DNA molecules from different sources into the one molecule in a test tube. Thus, the abilities or the phenotype of the organism, or the proteins it produces, can be altered through the modification of its genes. The term generally does not cover organisms whose genetic makeup has been altered by conventional cross breeding or by "mutagenesis" breeding, as these methods predate the discovery of the recombinant DNA techniques. Technically speaking, however, such techniques are, by definition, genetic modification. Rationale: Terminator Technology is the colloquial name given to proposed methods for restricting the use of genetically modified plants by causing second generation seeds to be sterile. The technology was under development by the U.S. Department of Agriculture and Delta and Pine Land Company in the 1990s and is not yet commercially available. Because some stakeholders expressed concerns that this technology might lead to dependence for poor smallholder farmers, Monsanto, an agricultural products company, pledged not to commercialize the technology even if and when is becomes commercially available. Reading 11: Genetic manipulation – terminator Complete reference: http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/Steinbrecher.htm The Ecologist, Sept-Oct 1998 v28 n5 p276(4), Terminator Technology: the threat to world food security. Ricarda A. Steinbrecher; Pat Roy Mooney. Author's Abstract: COPYRIGHT 1998 The Ecologist (UK). Abstract: According to Steinbrecher and Mooney (1998:276) in The Ecologist 28(5) “Monsanto's latest flagship technology makes a nonsense of its claim that it seeks to feed the worlds hungry. On the contrary, it threatens to undermine the very basis of traditional agriculture - that of saying seeds from year to year. What's more, this "gene cocktail" will increase the risk that new toxins and allergens will make their way into the food chain”. Rationale: Because of the relevant importance of genetic manipulation in agriculture, we have decided to include this article dealing with the controversial manipulation of agricultural products and the responses it has evoked the last few years. Reading(s) #1 Reading(s) #1.1 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Botany/Print version From Wikibooks, the open-content textbooks collection < Botany Note: current version of this book can be found at http://en.wikibooks.org/wiki/Botany Table of contents Introduction Introduction << Contents Page Introduction to the Botany Study Guide This Study Guide to the Science of Botany is a textbook at Wikibooks shelved under Biology and intended to establish a course of study in the subject of Botany, utilizing articles provided in Wikipedia (http://www.Wikipedia.org/) , with links to other relevant web sites and other Wikibooks as appropriate. In some cases, portions of the text from Wikipedia articles have been used to materially develop introductory text within the Guide. For the new user, it need be pointed out that Wikipedia differs from a standard encyclopedia in two important respects: 1) it is a hypertext document, and 2) it is open and editable, and therefore constantly changing. For the student following this or any guide through Wikipedia to cover a specific subject, it is recommended that each article (page) be read first in its entirety, before any hyperlinks are followed to other topics or explanations. It is too easy, otherwise, to simply become lost in a maze of links, and miss the main thrust of an article presented as an assignment from the Guide. Because Wikipedia is constantly changing (and, it is believed, improving) the quality of each article encountered will be variable. Some articles are well written and go to adequate depth, whereas others, lacking a proponent, are shallow and incomplete. Short or sloppy looking articles may contain questionable facts. These short-comings should diminish with time, but can be a problem for the student. One clear advantage to using this Guide linked to a hypertext like Wikipedia is the "circular redundancy with serendipity" factor that arises when an article is read and its hyperlinks followed; this factor can be a powerful learning tool. The persistent reader is subjected to a fairly high degree of repetitive reading, often presenting slightly differing perspectives on the same general topic, with the result that learning comes from redundancy and seeing difficult concepts presented in more than one way. At the same time, some hyperlinks lead down less relevant paths, bringing new and unanticipated knowledge. If, as a student, you are truely interested in mastering the subject of botany, you must be prepared to read beyond the basic assignments; in some cases, beyond Wikipedia to explore other, "outside" web sites. 1 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version It seems likely that the typical user of the Study Guide to the Science of Botany is not necessarily an active student taking a course in botany at the highschool (AP) or college level, but a person with a strong interest in plants—an amateur naturalist or a gardener. Therefore the guide must incorporate both the basic biological and physiological aspects of plants as well as extensive taxonomy-based coverage of the diversity of plants and related organisms. The amount of material now available on the web covering the latter subject is becoming nothing short of phenomenal. In effect, one now has access to much of the world's plant diversity, with photographs and descriptions, in many cases from web sites maintained by specialists. One goal of the guide is to provide a systematics-based approach to capturing this kind of information, hopefully giving the student a strong background in plant systematics. The importance of this approach is not that everyone should become a taxonomist—or become more familiar with plant taxonomy, a specialized field of botanical science with a relatively narrow following—but that appreciation for (and understanding of) species diversity is most critical at this time in our earth's history marked by accelerated species extinctions and destruction of native ecosystems by both human population expansion and man-induced spread of non-native species. The Study Guide to the Science of Botany includes two other "parallel" documents intended to enhance the usefulness of the Guide. These could also be used separately or independently as source documents for a beginning course in Botany. They are the Discussion pages and the Laboratory Exercise pages. Both are explained in detail in the next Section titled How to use this Guide. How to use << Contents Page How to Use the Botany Study Guide The purpose of the Study Guide to the Science of Botany is to weave—out of the information on Life Science and especially Botany contained in Wikipedia—a course of study for the student or layman. It is anticipated that this course will be either supplemental to instruction being received at a school or college, or will be self-directed. In either case, the Guide is not a novel and should not be approached as one. A smooth flow of dialogue is simply not possible and should not be anticipated. The Guide may be closer to the sometimes disjointed notes generated by a student from a lecture or careful reading of a detailed textbook. Within each subsection of a Chapter, introductory text is followed by one or more "reading assignments" of the form: Read Botany (Links need not be pursued at this time) Following (that is clicking on) the link (to Wikipedia "Botany" in this case) will open an article intended to provide the details of the Chapter subsection. Recommended articles should be read from top to bottom, and then re-read following some or all of the links embedded in the article to other articles for expanded elucidation or to clarify terms; that is, in most cases, completion of an "assignment" (recommended article) includes at least some or all articles linked to the first. Obviously, it cannot be the case that all links are followed to articles, whose links are then followed to articles, and so on until no new material is encountered. It is likely there would be no quick end to such a pursuit. The amount of time spent wandering beyond the original article is partly a personal matter of how much the reader is getting out of the foray than anything else. Realize it is certainly possible to wander well off the subject at hand. As in the example above, notes are provided with assignments giving some direction for pursuing links. An instruction NOT to follow links simply means the additional material will be encountered later in the course of instruction, and going beyond 2 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version the assigned article may provide too much detail for a beginning student. The following example: Read Science (The following links are included:) Scientific Method Philosophy of Science specifies that two other links ARE part of the assignment. Other links encountered may be followed to expand your knowledge or, as always, to aid in understanding of technical terms encountered. Hyperlinks included with the text in the Guide are there simply for convenience, usually to topics somewhat peripheral to the main one. In all cases, finding your way back to the Guide may become tricky, but we have to leave this up to you to establish, beyond pointing out that your browser's Back button is intended for this purpose. Discussion Questions At the end of each subsection are posted one to several questions. In general, you will get more out of these questions if you write out your answer on a piece of paper. You may wish to accomplish this on the re-read, allowing each question to guide your quest for an answer. A discussion page for each chapter provides answers to the questions posed. However, the questions are intended to be thought-provoking, and may not have a single straight-forward answer. Answers on the discussion pages are also necessarily much longer than would be expected of any one student; it is expected that each student answer will fit somewhere within the broad discussion presented. Laboratory Exercises A natural sciences course laboratory unit is supposed to provide hands-on experience in exploring topics raised in the text and lecture units. The best that a website can give towards this goal is a manual that is liberally provided with pictures and diagrams. The student must provide the "hands on" from the neighboring natural world. Fortunately, in botany, this is much easier to accomplish than in almost any other field of science. Both the outdoors, the local market, and (if available) a botanical garden can be sources of materials for study. Indeed, we may teach the structure of a pome using an apple in the hope that the student will end up with a pear. In using any of the Laboratory Exercises, it is always best to read through the entire module before actually doing anything. Resist the temptation to view the material as an instruction manual to be followed in a specific order. For one thing it is difficult to write a module that covers, at each step, all that the student should know before proceeding on to the next step. The value of any exercise will be significantly enhanced if you have a pretty good idea where it is going in advance. General Navigation The Study Guide is divided into Sections and Chapters which define the subject material of each module. At the bottom of each text page (main text of a module), is a short version of the Table of Contents, allowing the reader to jump between chapters within a Section. Here is an example of the "Wiki Contents Table" for Section I: Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells 3 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology Note that at the beginning of each module, links are provided to both the previous chapter and the suceeding chapter, as well as to the main Table of Contents. Links to units associated with a module, as for example to a Laboratory Exercise, appear near the end of the module Final Note As a final note, read the next Section and consider how you might make a contribution to the Guide.Botany Both this Guide and all articles in Wikipedia are free content that can be added to or edited by anyone. It is an opportunity for the user of these documents to contribute information, or even state given information more clearly, simply by editing a page. As a student with a textbook and a lecturer (teacher), you may find yourself in possession of useful facts, another point of view on existing facts, or a report you prepared of exceptional quality. Any of these can be added to an appropriate page in this Guide or the Wikipedia. However, this caution is strongly advised: Do not place into the Guide any text or pictures taken verbatim (or close to verbatim) from a text book, web site, or other copyrighted source without permission of the copyright holder. In general, this means, anything you submit should be your own work. To learn how to edit or contribute material to this textbook, first read the introduction at: How to Edit. << Contents Page | Chapter 1 | Chapter 2 >>| Chapter 1. Introduction to Botany Botany as a Science Botany is the branch of biology concerned with the scientific study of plants. Traditionally, botanists studied all organisms that were not generally regarded as animal. However, advances in our knowledge about the myriad forms of life, especially microbes (viruses and bacteria), have led to spinning off from Botany the specialized field called Microbiology. Still, the microbes are usually covered in introductory Botany courses, although their status as neither animal nor plant is firmly established. The earth star fungus (Geastrum aff. welwitschii). Click here to enlarge image Read Biology (Links need not be pursued at this time) Read Botany (Links need not be pursued at this time) and note that other texts encompassing topics in Biology are available (under development) at 4 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version WikiBooks as sources of reference. Plants are living entities, and material presented within Biology will have relevence here, most particularly at the cellular and subcellular levels of organization (Chapter 2). Both plants and animals deal with the same problems of maintaining life on planet Earth — their approaches seem quite different, but the end result is the same: continued existence in an organized state, as part of a universe whose tendency is towards greater disorganization. Back on Earth, however, it is a fact that microbes, plants, and animals comprise a very interdependent system. We divide them apart, because our minds work best that way. We categorize and learn common features or properties of the categories. This approach is neither right nor wrong, but is clearly efficient for our minds. Nonetheless, it is desirable to regularly step back and realize that the boundaries between categories are often just constructs, and exceptions to our categories usually abound. It was alluded to in the opening definition that Botany is a science. Just what makes Botany, or anything else a science? It is important to acquire a grasp of the fundamentals of science itself to fully appreciate both how botanical knowledge was gained as well as how it can be used. It is usually quickly disinteresting to acquire facts simply for the sake of knowing. Humans do not just appreciate mountains because they are there, they climb them because they are there! Read Science (The following links are included:) Scientific Method Philosophy of Science Read Why study science? (http://www.people.virginia.edu/~rjh9u/studysci.html) Questions: 1-1. Do you think the scientific method is something only a scientist would use? Living Systems Biology is defined as the study of life, and Botany is that discipline within Biology concerned with the study of living organisms called plants and with certain other living things that are not plants (but are not animals either). Defining 'Plant' Like many words in common usage that apply to biological entities or concepts, the term plant is more difficult to define than might be at first obvious. Although botanists describe a Kingdom Plantae, the boundaries defining members of Plantae are more exclusive than our common concept of a "plant". We are tempted to regard plant as meaning a multicellular, eukaryotic organism that generally does not have sensory organs or voluntary motion and has, when complete, a root, stem, and leaves. However, botanically only vascular plants have a root, stem, and leaves, and even some vascular plants, such as certain carnivorous plants and duckweed, fall afoul of that definition. But to be fair, the vascular plants are the plants we tend to encounter every day and that most people would readily regard as "plants". A more significant point of departure between Plantae and plants occurs among the seaweeds. Technically, only a relatively minor group of seaweeds (the chlorophytes or green algae) are members of the Kingdom Plantae. The majority of seaweeds, like the kelps (very large brown algae from the Order Laminariales), despite a superficial appearance of such, lack true stems, leaves, roots, and any kind of vascular systems as found in higher plants. Thus, the kelps are not Plantae; but are they plants? Certainly if we regard the green algae as plants, it is difficult to exclude the more prominent red and brown algae of our coastal waters. 5 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Another, much broader definition for plant is that it refers to any organism that is photoautotrophic—produces its own food from raw inorganic materials and sunlight. This is not an unreasonable definition, and is one that focuses on the role plants typically play in an ecosystem. However, there are photoautotrophs among the Prokaryotes, specifically photoautotrophic bacteria and cyanophytes. The latter are sometimes called (for good reasons) blue-green algae. Then there arises the problem that many people would consider that a mushroom is a plant; a mushroom is the fruiting body of a fungus (Kingdom Fungi) and not photoautotrophic at all, but saprophytic. However, there are more than a few species of flowering plants, fungi, and bacteria that are not autotrophic, but parasitic. We cannot hope to offer a firm answer. The list of characteristics that separate the Plantae from the other biological kingdoms provides at least a technical definition, but realize it is only a technical definition. The problem this lack of precision or agreement in the definition of "plant" presents is one of understanding statements, often encountered in Wikipedia (and other) articles, of the sort: ...xylem is one of the two transport tissues of plants. In general it cannot be assumed this means all plants, algae through flowering plants. It very probably does not include fungi or bacteria. Indeed, it is usually safest to assume the discussion is about vascular plants (essentially the ferns, conifers, flowering plants, and a few others; see discusion below on "General Terminology") unless stated differently (e.g., ...in vascular and non-vascular plants this is such and such). Plants as Organisms Read Organism (Links need not be pursued at this time) Read Plants (Links need not be pursued at this time) The distinction between life and non-life is not as easily made as you might think. There exist intracellular "parasites" that are progressively less alive in terms of being metabolically active: Viruses — Viroids — Prions Questions: 1-2. What things do all plants seem to have in common that would justify our classifying them together in their own Kingdom? 1-3. When you catch a cold a virus has infected your body. Why do you think there is reason to question whether the virus is living or not? After all, if you took some ricinin (a plant poison), you would get very sick, but no one would suggest the toxin were alive or that the plant had entered your body. Plants and their Uses There can be no disputing the fundamental significance of plants to the ecology of our planet. Photosynthetic plants utilize energy arriving from the sun to create complex organic molecules from inorganic substances, and by this process contribute oxygen to the atmosphere. Advanced animal life is very much dependent upon this source of oxygen, as well as the organic molecules that form the basis of nearly every food web on the planet. However, humans utilize plants in many ways, especially as sources of pleasure, food, and material for shelter, clothing, and more. Consider here the role plants play in our everyday lives and in our economy. 6 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks Read Read Read Read Horticulture (Links need not be pursued at this time) Gardening (Links need not be pursued at this time) Agriculture (Links need not be pursued at this time) Silviculture (Links need not be pursued at this time) http://en.wikibooks.org/wiki/Botany/Print_version There is a Wikibook COOKBOOK There is a Wikibook on GARDENING Introduction to Plant Classification At the beginning of this chapter it was suggested that each of us categorizes information we encounter on a daily basis. Our minds seem to want to find relationships between facts and observations, to erect mental bins in which to place new items with previous "facts". This natural human process is the basis for prejudice, in as much as "facts" categorized together can become strongly associated. But these are personal constructs. In order for scientists of many races, speaking many languages, and coming from all manner of backgrounds and experiences to work productively together to solve common problems, the objects with which they work must be classified within a universally accepted framework. The classification of living things is called systematics, or taxonomy, and ideally should reflect the evolutionary history (phylogeny) of the different organisms. Read The evolutionary timeline to gain an understanding of how evolutionary history has played out on the planet earth, paying particular attention to entries in the table that describe the early evolution of life and the later evolution of terrestrial plant life. Taxonomy arranges organisms in groups called taxa, while systematics seeks clues to their relationships. The dominant system of Scientific Classification is called Linnaean taxonomy, and includes classification ranks as well as an organism naming convention called binomial nomenclature. Traditionally, all living things were divided into five kingdoms: Monera — Protista — Fungi — Plantae — Animalia However, this five-kingdom system has been replaced by Carl Woese's three-domain system, which focuses on phylogenic roots and comparison of DNA structures. The older approach utilized visual observation as the basis of classification. The three domains reflect whether cells have nuclei (eukaryotic) or not (prokayotic), as well as differences in cell membranes and cell walls. Archaea — Eubacteria — Eukaryota Read Binomial nomenclature Read Scientific classification Recall (and review as necessary) how these groupings relate to the sequence of events in the evolutionary history of life as summariaed in Timeline of Evolution. You will return to the subject of Scientific Classification to consider in much more detail the groups of organisms studied in Botany, beginning with Chapter 7. First, however, we shall turn our attention to the structure and function of cells and eventually to gain an understanding of plant structure (plant anatomy) and function (plant physiology). General Terminology In Section II of this text we will delve much deeper into "plant" systematics. But you should be aware of some general terms related to classificatory schemes that are used regularly in discussing plants. You have probably encountered these terms many times, although may not be aware of their exact definitions. For 7 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version example, much of the material in Section I of this textbook is biased towards flowering plants. That is, much of the descriptive material here as well as at Wikipedia refers specifically to these. Flowering plants are angiosperms; plants that have flowers and produce seeds, and comprise the majority of the plants we would normally encounter in say a nursery if not on the street, field, or empty lot. Seed-bearing plants include both the angiosperms and the gymnosperms, the latter now treated as a modern group called conifers. The conifers are also common plants, especially in higher latitudes, but bear cones instead of flowers. Both conifers and flowering plants develop vascular tissues internally that conduct fluids (especially water) throughout the plant. Included in the vascular plants are ferns. Ferns have vascular tissue, but reproduce by spores. They do not produce seeds and do not bear flowers. Laboratory Excercises for Chapter 1 >> Discussion of questions for Chapter 1 >> Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology << Contents Page | << Chapter 1 | Chapter 2 | Chapter 3 >>| Chapter 2. Plant Cells Introduction A cell is a very basic structure of all living systems, consisting of protoplasm within a containing cell membrane. Only entities such as viruses—literally on the boundary between non-living chemicals and living systems—lack cells or basic cell structure. All plants, including very simple plants called algae, and all animals are made up of cells, and these are organized in various ways to create structure and function in an organism. Biologists recognize two basic types of cells: prokaryotic and eukaryotic. Prokaryotic cells are structurally more simple. They are found only in single-celled and some simple, multicellular organisms (all bacteria and some algae, which all belong to Bacteria and Archaea domains). Eukaryotic cells are found in most algae, all higher plants, fungi, and animals (Eukarya domain). Thus, differences between these two cell types are critical to how an organism is classified, and an important consideration in the evolutionary sequence of life on the planet Earth. A lupe (left) and a hand-lens (right) tools used by botanists in the field Plant Cell Structure Nearly all cells are too small to be seen with the unaided eye. As always there are some exceptions, but 8 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version generally magnification is required to detect a cellular structure. In plants, a good hand-lens or lupe (see photo at right) will sometimes suffice, but in working with cells or observing how cells are organized to form tissues and structures, a high power microscope is used. Read about Cells ~ You may wish to follow some or all links to "Main articles" as these provide detail that may interest you; or you might return to explore further should questions arise later in the course. Read Plant cells and, at minimum, articles at the following links (but ignore, for now, the topic of Plant Cell Types): Cell Wall Protoplasm and cytoplasm Vacuole Ergastic substances Plastids Chloroplasts Also note that the textbook, Cell Biology, is available at WikiBooks and can be used as a more detailed reference. You should read the Introductory Chapter (all subsections) at this time. Questions: 1. Can you think of reasons why macroscopic organisms are multicellular? (Macroscopic means large, in the sense of "not microscopic") Basic Cell Function You should, by now, have a general appreciation for the complexity of cellular structure. Improvements in microscopy, especially development of the Electron microscope, have revealed that cells are not merely membranous sacks containing fluid of gel-like consistency. The degree of organization of the cytoplasm into organelles and their membranes should have you convinced that much (perhaps most) of what is really going on around you on this planet is occurring at a scale that is simply inaccessable to your eyes. And while you cannot be expected to directly observe chemical reactions at a molecular scale, contemplate that you cannot, even with powerful optics, directly observe most of the structure where these reactions are somehow controlled to produce outcomes favorable to life—indeed, are life. Hopefully, as you acquire knowledge and become a biologist—a botanist—you will learn to recognize the relevant phenomena by their macroscopic expressions (that which you can readly observe with the unaided eye). To appreciate basic cell function, it is necessary to first list the processes or outcomes that cells must accomplish to further existence. More specialized functions will be discussed under plant cell structure, as our interest must eventually focus on plants. For now, recall that in your reading you have already encountered these several basic abilities of cells: Metabolism involves taking in of raw material to use in building cell components and breaking down of other molecules to provide energy for various growth processes; byproducts may be released. Protein biosynthesis by transcription of DNA to RNA and then translation to protein, used in growth or released for use elsewhere by the organism. Reproduction by cell division. Now explore each in turn. Think initially of a single-celled organism with no special abilities, only a "will" to stay alive and perpetuate itself. Remember, the environment will not be kind. The cell must grow and reproduce to counter the tendency of outside forces to breakdown molecular structure and destroy life. Then consider the situation where a cell is part of a multicellular organism, and may be performning more limited and specialized functions. Read Cell metabolism (Follow links and read at least these articles): 9 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Metabolic pathway (Links need not be followed) Cell respiration (Follows all links) Read Protein biosynthesis (Follow links as necessary to understand process and terminology; Also included is:) Gene expression Read Cell reproduction (The following links are included:) Mitosis Cell cycle Questions: 1. Have you been able to discern a relationship between genes and basic cell function? If so, is this also a basic cell function, and where do we list it? Plant Cell Specializations We will learn about the cells of algae and other organisms (e.g., bacteria and fungi) traditionally covered within Botany in later chapters on those organsims (Chapters 5 - 7). Here, we concentrate on the cells of plants. The simplest type of plant cell is called a parenchyma cell and most of the basic metabolic and reproductive processess of the plant occur in these cells. A term for parenchyma cells with chloroplasts, is chlorenchyma cells. Other plant cell types that we shall be considering are: Collenchyma ~ living cells with thickened walls for increased support Sclerenchyma ~ lignified dead cells forming fibers for increased support Epidermal ~ surface covering Cork Xylem tracheid ~ single long (up to 1 mm) thin cells for transporting water and support Xylem vessel ~ cells form individual elements in an even longer (up to 1 meter in extreme cases) tube for transporting water Meristematic cells ~ growth Read Parenchyma cell Laboratory Exercises for Chapter 2 >> Discussion of questions for Chapter 2 >>> Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology << Contents Page | << Chapter 2 | Chapter 3 | Chapter 4 >>| Chapter 3. Plant Tissues 10 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Introduction Plant Tissues Most plant cells are specialized to a greater or lesser degree, and arranged together in tissues. A plant tissue can be simple or complex depending upon whether it is composed of one or more than one type of cell. The simplest tissue found in plants is called parenchyma. The cells are not very specialized, more or less rounded or angular where packed together, and thin-walled. A type of parenchyma called chlorenchyma because the cells contain chloroplasts forms tissue (usually in the leaves) responsible for most of the photosynthesis occurring in the plant. Note that in simple tissues at least (tissues comprised mostly of one cell type), the tissue name follows from the cell type. However, tissues may also have unique anatomical names related to where in the plant they occur. Meristems The growth of a plant requires a source of undifferentiated cells located in places where growth is needed and can be initiated to further the body plan (in comparison to animals, plants are rather open in this regard). Some enlargement in size is always possible by elongation or enlargement of existing cells, or by existing cells simply dividing. But differentiation of one cell type into another is only possible if the initial cell (mother cell) is not very specialized. Tissues comprised of cells that remain undifferentiated and supply, by their divisions, cells to form new tissues and organs, are called meristems. Meristem tissue occurs in places that allow for a very orderly pattern of growth. Read Meristems Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology << Contents Page | << Chapter 3 | Chapter 4 | Chapter 5 >>| Chapter 4. Plant Vegetative Organs Introduction As was noted in the previous chapter, most plant cells are specialized to a greater or lesser degree, and arranged together in tissues. A tissue can be simple or complex depending upon whether it is composed of one or more than one type of cell. Tissues are further arranged or combined into organs that carry out life 11 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version functions of the organism. Plant organs include the The parrot's feather, an aquatic plant (Myriophyllum aquaticum) Click to enlarge picture leaf, stem, root, and reproductive structures. The first three are sometimes called the vegetative organs and are the subject of exploration in this chapter. Reproductive organs will be covered in Chapter 5. The relationships of the organs within a plant body to each other remains an unsettled subject within plant morphology. The fundamental question is whether these are truly different structures, or just modifications of one basic structure (Eames, 1936; Esau, 1965). The plant body is an integrated, functional unit, so the division of a plant into organs is largely conceptual, providing a convenient way of approaching plant form and function. A boundary between stem and leaf is particularly difficult to make, so botanists sometimes use the word shoot to refer to the stem and its appendages (Esau, 1965). The Leaf The plant leaf is an organ whose shape promotes efficient gathering of light for photosynthesis, but the form of the leaf must also be balanced against the fact that most of the loss of water a plant might suffer is going to occur at its leaves. Leaves are extremely variable in details of size, shape, and adornments like hairs. Read: Leaf (By now, the links you encounter in this article should be known to you; follow any link terms you do not understand) Although the leaves of most plants carry out the same very basic functions, there is nonetheless an amazing variety of leaf sizes, shapes, margin types, forms of attachment, ornamentation (hairs), and even color. Examine the Leaves (forms) page to learn the extensive terminology used to describe this variation. Consider that there are functional reasons for the modifications from a "basic" type. The Stem The stem arises during development of the embryo as part of the hypocotyl-root axis, at the upper end of which are one or more cotyledons and the shoot primordium. Read: Stem The Root The root is the (typically) underground part of the plant axis specialized for both anchoring the plant and absorbing water and minerals. Read: Root (Follow any links for terms you do not understand and to gain a complete picture of root structural variation) Be sure to read about and understand the meaning of each (at a minimum) of the following terms: adventitious roots, endodermis, epidermis, gravitropism, root cap, root hair, stele, taproot. Most of the material you have read discusses the root organ as found in the angiosperms (flowering plants). However, among the vascular plants, only Psilotales lack such an organ, having instead rhizomes that bear hair-like absorbing structures called rhizoids (Eames, 1936 in Esau, 1965). Questions: 12 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version 4-1. At this point the conceptual differences between cell types, tissues, organs, and organisms may be somewhat confusing. Using the leaf as an example, describe this structure in a way that considers the cell types, tissues, and organs for that part of the leaf where photosynthesis is concentrated. Laboratory Excercises for Chapter 4 >> Discussion of questions for Chapter 4 >>> Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology << Contents Page | Chapter 4 | Chapter 5 | Chapter 6 >> Chapter 5. Plant Reproduction Vegetative Reproduction Vegetative reproduction is asexual reproduction—other terms that apply are vegetative propagation or vegetative multiplication. Vegetative growth is enlargement of the individual plant; vegetative reproduction is any process that results in new plant "individuals" without production of seeds (see The Seed below) or spores. It is both a natural process in many, many species as well as one utilized or encouraged by horticulturists and farmers to obtain quantities of economically valuable plants. In this respect, it is a form of cloning that has been carried out by humankind for thousands of years and by "plants" for hundreds of millions of years. Noni (Morinda citrifolia) flowers and fruit, Note stages of progressive maturation shown from a cluster of flowers to an accessory fruit Read Vegetative Reproduction (Follow all links) Sexual Reproduction The Flower The flower is the reproductive organ of plants classified as angiosperms—that is, the flowering plants comprising the Division Magnoliophyta. All plants have the means and corresponding structures for 13 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version reproducing sexually, and these other cases will be explored in later chapters. However, because flowering plants are the most conspicuous plants in almost all terrestrial environments, we justifiably devote this chapter to the flowering plants alone. You will learn how other plant groups (and non-plant groups, such as fungi) reproduce sexually in Section II of the The Guide. The basic function of a flower is to produce seeds through sexual reproduction. Seeds are the next generation, and serve as the primary method in most plants by which individuals of the species are dispersed across the landscape. Actual dispersal is, in most species, a function of the fruit: structural parts that typically surround the seed. But the seed contains the germ of life of the next generation. Read Plant sexuality (Follow links you find interesting, concentrating on acquiring a grasp of the terminology) Read The Flower (Follow links you find interesting, but at minimum read each of the following articles) Read calyx - the sepals Read corolla - the petals Read androecium - the stamens Read gynoecium - the pistil(s) Be sure to read about and understand the meaning of each of the following terms: androecium, anthesis, calyx, carpel, corolla, gynoecium, inferior ovary, nectary, perigynous, petal, pistil, pollen, sepal, stamen, superior ovary, syncarpous. Read Inflorescence Be sure to read about and understand the meaning of each of the following terms: bract, inflorescence, panicle, raceme, spadix, spikelet. Questions: 5-1. Do you think the flower structure is in any way responsible for the considerable success of flowering plants in populating the earth? The Seed and Germination the primary purpose of the seed is one of preserving the continuity of life—starting a new generation in a new physical location. For large plants (shrubs and trees), this can be especially important because successful germination and growth close to the parent may be difficult or impossible; the established plant monopolizes light and water resources in its immediate vicinity. Seeds can also serve the function of overwintering or surviving harsh conditions. The entire generation—every individual—may die in the Fall or the dry season. In many annual species, only the seed exists during unfavorable dry or cold conditions. The Seed (Follow all links on anatomy and function) Read Germination The Fruit The fruit is the actual agent of dispersal in most flowering plants. The Fruit Laboratory Excercises (flowers) for Chapter 5 >> Laboratory Excercises (seeds) for Chapter 5 >> Discussion of questions for Chapter 5 >> 14 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Botany Study Guide ~ Wiki Contents Table Section I Chapter 1 - Introduction ~ Chapter 2 - Plant cells Chapter 3 - Plant Tissues ~ Chapter 4 - Plant Organs Chapter 5 - Plant Reproduction ~ Chapter 6 - Plant Morphology Chapter 5. Plant Reproduction Laboratory ~ Flowers An orchid flower This first laboratory excercise for Chapter 4 deals with the flowers of a ground orchid from Southeast Asia. The photograph on the right demonstrates the descriptive terminology that can be applied to this species. You may wish to read about orchids to place this plant taxonomically and better understand unusual aspects of the structure of this flower. In reading the description below, be sure you understand how or why each bolded word applies to this specimen. Also, observe that the flowering-through-fruiting sequence is well demonstrated in the photograph because each flower is in a slightly different phase of its life cycle from bud to fruit. Spathoglottis plicata Blume — The flowers of this orchid are carried on an erect raceme Infloresence of the orchid, Spathoglottis plicata (enlarge to examine). growing out of the pseudobulb, each flower subtended by a green to purplish bract that becomes strongly reflexed with age. The purple sepals and petals are similar and spreading, elliptic to elliptic-ovate; the labellum is in three distinct parts: the lateral lobes narrow and erect, the middle lobe horizontal and cleft or 2-lobed. Lying above the latter is the narrowly clavate column. The inferior ovary in Spathoglottis develops into a cylindrical capsule (fruit) as the perianth withers. 4-1. Review the photograph of the inflorescence of the orchid. Which one of these statements is true: a) this inflorescence demonstrates determinate growth b) this inflorescence could as well be called a spike c) the uppermost flower shows anthesis. d) there are five petals, therefore this is a dicot. Following are a series of photographs of flowers from various plants. Note that by clicking on the word 15 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version "Examine" in each title, you can enlarge the particular photograph for closer examination. Read each question and the offered answers carefully. All parts of answer choice must be correct for that choice to be correct. Photograph 1: Bidens torta (Examine) 4-2. The structure at B is: a) leaf b) corolla c) ligule d) sepal e) petiole 4-3. Although the flowers in these three photographs appear very different, the following parts or floral structures are essentially the same: a) AA and F b) BB and C c) G and H d) F and B e) D and BB 4-4. Which statement of the following applies to the structure indicated at E : Photograph 2. Hibiscus (Examine) a) Pollen grains have landed on this pistil b) Androecium of a monoecious plant c) This is a spathe d) E is an anther releasing pollen e) This flower head is on a dioecious plant << Return to Chapter 5 Answers to Chapter 4 Laboratory Questions: 4-1 ~ c (this flower alone is capable of pollination) 4-2 ~ b (A flower head with tubular disk corollas) 4-3 ~ d (both F and B indicate petals of their respective flowers) 4-4 ~ d (the androecium is supported on a tubular structure (G) that surrounds the pistil (H) Chapter 5. Plant Reproduction Laboratory ~ Seeds A monocot seedling 16 of 23 23/11/06 15:00 Botany/Print version - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Botany/Print_version Photograph 3. Xanthosoma or 'Ape (Examine) The photograph at the right shows two germinating seeds. These are seeds of the fan palm, Pritchardia remota, a species found naturally only on (endemic to) the remote island of Nihoa in the Hawaiian islands. The seed on the left is in the proper orientation in the planting medium (only a part of the fruit coat covering the seed is visible), while the one on the right (in a slightly earlier stage) has been laid on the surface in order to better reveal development of the root. The following structures are labeled: co - coleoptile or shoot pole of plant axis; essentially a cap within which the plumule (first leaf) is developing, to eventually project through as in the seedling on the left. ra - radicle; primordial root or root pole of axis (note tiny root cap), buried in the medium in the seedling on the left. sc - scuttelum; that part of the cotyledon that remains inside the seed to absorb food stored in an endosperm. (enlarge to examine). << Return to Chapter 5 License GNU Free Documentation License Version 1.2, November 2002 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. 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Privacy policy About Wikibooks Disclaimers 23 of 23 23/11/06 15:00 Reading(s) #1.2 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Cell Biology/Print version From Wikibooks, the open-content textbooks collection < Cell Biology Note: current version of this book can be found at http://en.wikibooks.org/wiki/Cell_Biology Remember to click "refresh" to view this version. Table of contents Introduction Size of cells What is a cell? What is the difference between elements? What is living? What is interesting about cell biology? Types of cells Prokaryotes Bacteria Eukaryotes Unique Properties of Plant Cells Parts of the cell Membranes Organelles Genetic material Energy supply (chloroplasts and mitochondria) Cell division Cell cycle Meiosis Mitosis Genes Expression Translation 1 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Introduction Size of cells Cell Biology | Introduction Size of cells | What is a cell >> Size of Cells Although it is generally the case that biological cells are too small to be seen at all without a microscope, there are exceptions as well as considerable range in the sizes of various cell types. Eukaryotic cells are typically 10 times the size of prokaryotic cells (these cell types are discussed in the next Chapter). Plant cells are on average some of the largest cells, probably because in many plant cells the inside is mostly a water filled vacuole. So, you ask, what are the relative sizes of biological molecules and cells? The following are all approximations: 2 of 32 Cells are so small that even a cluster of these cells from a mouse only measures 50 microns 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version 0.1 nm (nanometer) diameter of a hydrogen atom 0.8 nm Amino Acid 2 nm Diameter of a DNA Alpha helix 4 nm Globular Protein 6 nm microfilaments 10 nm thickness cell membranes 11 nm Ribosome 25 nm Microtubule 50 nm Nuclear pore 100 nm Large Virus 150-250 nm small bacteria such as Mycoplasma 200 nm Centriole 200 nm (200 to 500 nm) Lysosomes 200 nm (200 to 500 nm) Peroxisomes 800 nm giant virus Mimivirus 1 µm (micrometer) (1 - 10 µm) the general sizes for Prokaryotes 1 µm Diameter of human nerve cell process 2 µm E.coli - a bacterium 3 µm Mitochondrion 5 µm length of chloroplast 6 µm (3 - 10 micrometers) the Nucleus 9 µm Human red blood cell 10 µm (10 - 30 µm) Most Eukaryotic animal cells (10 - 100 µm) Most Eukaryotic plant cells 90 µm small Amoeba 100 µm Human Egg up to 160 µm Megakaryocyte up to 500 µm giant bacterium Thiomargarita up to 800 µm large Amoeba 1 mm (1 millimeter, 1/10th cm) 1 mm Diameter of the squid giant nerve cell 120 mm Diameter of an ostrich egg (a dinosaur egg was much larger) 3 meters Length of a nerve cell of giraffe's neck Related reading Some early history related to the development of an understanding of the existence and importance of cells. The importance of microscopy. What limits cell sizes? Prokaryotes - Limited by efficient metabolism Animal Cells (Eukaryotic) - Limited by Surface Area to Volume ratio Plant Cells (Eukaryotic) - Have large sizes due to large central vacuole which is responsible for their growth Size of cells | What is a cell >> Cell Biology | Introduction |What is a cell? Cell biology | Introduction << Size of cells | What is a cell | What is the difference between elements >> 3 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Cells are the fundamental building blocks of life. Cells vary to form individual "single-cell" organisms (bacteria) to "multi-cellular" structures (tissue, organs) and organisms (animals and plants). Cells are structural units that make up plants and animals; also, there are many single celled organisms. What all living cells have in common is that they are small 'sacks' composed mostly of water. The 'sacks' are made from a phospholipid bilayer membrane. This membrane is semi-permeable (allowing some things to pass in or out of the cell while blocking others). There exist other methods of transport across this membrane that we will get into later. Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles So what is in a cell? Cells are 90% fluid (called cytoplasm) which consists of free amino acids, proteins, carbohydrates, fats, and numerous other molecules. The cell environment (i.e., the contents of the cytoplasm and the nucleus, as well as the way the DNA is packed) affect gene expression/regulation, and thus are VERY important aspects of inheritance. Below are approximations of other components (each component will be discussed in more detail later): Elements 59% Hydrogen (H) 24% Oxygen (O) 11% Carbon (C) 4% Nitrogen (N) 2% Others - Phosphorus (P), Sulphur (S), etc. Molecules 50% 15% 15% 10% 10% protein nucleic acid carbohydrates lipids Other Components of cytoplasm Cytosol - contains mainly water and numerous molecules floating in it- all except 4 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version the organelles. Organelles (which also have membranes) in 'higher' eukaryote organisms: Nucleus (in eukaryotes) - where genetic material (DNA) is located, RNA is transcribed. Endoplasmic Reticulum (ER) - Important for protein synthesis. It is a transport network for molecules destined for specific modifications and locations. There are two types: Rough ER - Has ribosomes, and tends to be more in 'sheets'. Smooth ER - Does not have ribosomes and tends to be more of a tubular network. Ribosomes - half are on the Endoplasmic Reticulum, the other half are 'free' in the cytosol, this is where the RNA goes for translation into proteins. Golgi Apparatus - important for glycosylation, secretion. The Golgi Apparatus is the "UPS" of the cell. Here, proteins and other molecules are prepared for shipping outside of the cell. Lysosomes - Digestive sacks found only in animal cells; the main point of digestion. Peroxisomes - Use oxygen to carry out catabolic reactions, in both plant and animals. In this organelle, an enzyme called catalase is used to break down hydrogen peroxide into water and oxygen gas. Microtubules - made from tubulin, and make up centrioles,cilia,etc. Cytoskeleton - Microtubules, actin and intermediate filaments. Mitochondria - convert foods into usable energy. (ATP production) A mitochondrion does this through aerobic respiration. They have 2 membranes, the inner membranes shapes differ between different types of cells, but they form projections called cristae. The mitochondrion is about the size of a bacteria, and it carries its own genetic material and ribosomes. Vacuoles - More commonly associated with plants. Plants commonly have large vacuoles. Organelles found in plant cells and not in animal cells: Plastids - membrane bound organelles used in storage and food production. These are similar to entire prokaryotic cells - for example, like mitochondria they contain their own DNA and self-replicate. They include: Chloroplasts - convert light/food into usable energy. (ATP production) Leucoplasts - store starch, proteins and lipids. Chromoplasts - contain pigments. (E.g. providing colors to flowers) Cell Wall - found in prokaryotic and plant cells; provides structural support and protection. << Size of cells | What is a cell | What is the difference between elements >> Cell biology | Introduction What is elements? the difference between Cell biology | Introduction 5 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version << What is a cell | What is the difference between elements | What is living >> The various elements that make up the cell are: 59% Hydrogen (H) 24% Oxygen (O) 11% Carbon (C) 4% Nitrogen (N) 2% Others - Phosphorus (P), Sulphur (S), etc. The difference between these elements is their respective atomic weights, electrons, and in general their chemical properties. A given element can only have so many other atoms attached. For instance carbon (C) has 4 electrons in its outer shell and thus can only bind to 4 atoms; Hydrogen only has 1 electron and thus can only bind to one other atom. An example would be Methane which is CH4. Oxygen only has 2 free electrons, and will sometimes form a double bond with a single atom, which is an 'ester' in organic chemistry (and is typically scented). Methane Water H | H-C-H | H Methanol (Methyl Alcohol) H | H-C-O-H | H H H \ / O As for the organic molecules that make up a typical cell: 50% 15% 15% 10% 10% protein nucleic acid carbohydrates lipids Other Here is a list of Elements, symbols, weights and biological roles. 6 of 32 Element Symbol Atomic Weight Biological Role Calcium Ca 40.1 Bone; muscle contraction, second messenger Carbon C 12.0 Constituent (backbone) of organic molecules Chlorine Cl 35.5 Digestion and photosynthesis 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Copper Cu 63.5 Part of Oxygen—carrying pigment of mollusk blood. Fluorine F 19.0 For normal tooth enamel development Hydrogen H 1.0 Part of water and all organic molecules Iodine I 126.9 Part of thyroxine (a hormone) Iron Fe 55.8 Hemoglobin, oxygen animals Magnesium Mg 24.3 Part of chlorophyll, the photosynthetic pigment; essential to some enzymes. Manganese Mn 54.9 Essential to some enzyme actions. Nitrogen N 14.0 Constituent of all proteins and nucleic acids. Oxygen O 16.0 Respiration; part of water; and in nearly organic molecules. Phosphorus P 31.0 High energy bond in ATP. Potassium K 39.1 Generation of nerve impulses. Selenium Se 79.0 For the working of many enzymes. Silicon Si 28.1 Diatom shells; grass leaves. Sodium Na 23.0 Part of Salt; nerve conduction Sulfur S 32.1 Constituent of most proteins. Important in protein structure: Sulfide bonds are strong. Zinc Zn 65.4 Essential to alcohol oxidizing enzyme. caring pigment of many all << What is a cell | What is the difference between elements | What is living >> Cell biology | Introduction What is living? Cell biology | Introduction << What is the difference between elements | What is living | What is interesting about cell biology >> The question, "What is life?" has been one of many long discussions and the answer may depend upon your initial definitions. 7 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Some definitions of life are: 1. The quality that distinguishes a vital and functional being from a non-living or dead body or purely chemical matter. 2. The state of a material complex or individual characterized by the capacity to perform certain functional activities including metabolism, growth, and reproduction. 3. The sequence of physical and mental experiences that make up the existence of an individual. Under these definitions life may or may not include a virus that is only 'alive' if it can insert its genetic material into a living cell. To some, living systems that react to the environment, grow, improve, and reproduce are alive. A more liberal definition would include too much, a narrower one would not include all cells. << What is the difference between elements | What is living | What is interesting about cell biology >> Cell biology | Introduction What is interesting about cell biology? Cell biology | Introduction << What is living | What is interesting about cell biology What makes Cell Biology particularly interesting is that there is so much that is not fully understood. A cell is a complex system with thousands of molecular components working together in a coordinated way to produce the the phenomenon we call "life". During the 20th century these molecular components were identified (for example, see Human Genome Project), but research continues on the details of cellular processes like the control of cell division and cell differentiation. Disruption of the normal control of cell division can cause abnormal cell behavior such as rapid tumor cell growth. Cells have complex interactions with the surrounding environment. Whether it is the external world of a single celled organism or the other cells of a multicellular organism, a complex web of interactions is present. Study of the mechanisms by which cells respond appropriately to their environments is a major part of cell biology research and often such studies involve what is called signal transduction. For example, a hormone such as insulin interacting with the surface of a cell can result in the altered behavior of hundreds of molecular components inside the cells. This sort of complex and finely tuned cell response to an external signal is required for normal metabolism and to prevent metaboic disorders like Type II diabetes. Most of the cells of a multi-cellular organism have the same genetic material in every cell, yet, there are over 200 types of cells in the body that are different shapes, sizes and and carry out very different functions. And ALL of these cells were developed from one special cell, a zygote. The study of how the many cell types develop during 8 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version embryonic development (Developmental Biology) is a branch of Biology that is heavily dependent on the use of microscopy. Much of the control of cell differentiation is at the level of the control of gene transcription, the control of which mRNAs are made. Muscle cells make muscle proteins and nerve cells make brain proteins. Geneticists, molecular biologists and cell biologists are working to discover the details of how cells specialize to accomplish hundreds of functions from muscle contraction to memory storage. Summary Complexity in: inter-relations between cells signal transduction pathways inside cells control of cell death and cell reproduction control of cell differentiation control of cell metabolism. << What is living | What is interesting about cell biology Cell biology | Introduction Types of cells Prokaryotes Biology Cell biology | Types of cells Prokaryotes | Eukaryotes >> 9 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Most of these prokaryotic cells are small, ranging from 1 to 10 microns with a diameter no greater than 1 micron. The major differences between Prokaryotic and Eukaryotic cells are that prokaryotes do not have a nucleus as a distinct organelle and rarely have any membrane bound organelles [mitochondria, chloroplasts, endoplasmic reticulum, golgi apparatus, a cytoskeleton of microtubules and microfilaments] (the only exception may be a bacterium discovered to have vacuoles). Both types contain DNA as genetic material, have a surrounding cell membrane, have ribosomes[70 s], accomplish similar functions, and are very diverse. For instance, there are over 200 types of cells in the human body, that vary greatly in size, shape, and function. The structures of two prokaryotic cells. The Prokaryotes are cells without a distinct bacterium (shown at the top) is a heterotrophs, nucleus.They have genetic material but that organisms that eat other organisms. Cyanophytes are autotrophs, organisms that material is not enclosed within a membrane. make their food without eating other organisms. Prokaryotes include bacteria and cyanophytes. The genetic material is a single circular DNA strand and is located within the cytoplasm. Recombination happens through transfers of plasmids (short circles of DNA that pass from one bacterium to another). Prokaryoytes do not engulf solids, nor do they have centrioles or asters. Prokaryotes have a cell wall made up of peptidoglycan. Prokaryotes | Eukaryotes >> Biology_Cell_biology | Types of cells Bacteria Bacteria are prokaryotic, unicellular organisms. Bacteria are very small; so much so that 1 billion could fit on 1 square centimeter of space on the human gums, and 1 gram of digested food has 10 billion bacteria. Bacteria are the simplest living organisms. Previously they fell under the Kingdom Moneran, but now they fall into two different Kingdoms: Archaebacteria and Eubacteria. There are several differences between the two. Archaebacteria have no peptidoglycan in their cellular walls. They also have odd lipids in their cell walls. Many are able to live in extreme places (like early Earth). There are 3 types of Archaebacteria. The first type is Methanogen. These use Carbon dioxide and Hydrogen to make Methane. They are found in sewage, cows, and swamps, and they 10 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version do not take in oxygen. The second type is Extreme Halophile. These live in extremely salty places (i.e.: the dead sea and great salt lake). Finally, the third type is Thermoacidophiles. These prefer extremely hot, acidic areas (i.e.: hot springs and volcanos). Eubacteria have peptidoglycan in their cell walls, and they have no unusal lipids. They have three shapes: bacilli (hot dog shaped), cocci (ball shaped), and spirilli (spring shaped). Eubacteria can also have prefixes before their names: strepto, indicating chains of the shaped bacteria, and straphylo, indicating clusters of the shaped bacteria. Eubacteria are tested in labratories for Gram stains. Gram stains will determine if antibiotics will work (Gram postive) or if they will not (Gram Negative). There are four major types of Eubacteria: Cyanobacteria (green bacteria that infest fertilizer polluted ponds and lakes and mass produce algae), Spirochetes (Gram negative bacteria on which antibiotics do not work), Gram Positive (both gram positive that are used to make yogurt, streptthroat is one of these), and Proteobacteria (E-coli). Bacteria also have special structures: Plasmids (a small loop of DNA separate from the nuclear region, which is used for creating genetic variety, inserting into other organisms, and by genetic engineers) and Endospores (hard coat created by some bacteria in extreme conditions--this is why canning jars must be boiled for a long time). Reproduction is either through binary fusion (splitting of a cell with no variety in its genes) or through several other forms that produce genetic variety: Transformation (taking DNA from environment and incorparting it into themselves), Conjugation ("sex" in which cilia hook together and the Plasmids exchange genes), and transduction (viri infect the bacteria and the bacteria infects the virus with its Plasmid to move genes throughout the population). Bacteria produce poisons that can cause sickness: exotoxins, which are given off by the Gram positive bacteria, and endotoxins, which are given off by Gram negative bacteria as they die. Eukaryotes Cell biology << Prokaryotes | Eukaryotes | Plants >> Eukaryotes are cells with a distinct nucleus, a structure in which the genetic material (DNA) is contained, surrounded by a membrane much like the outer cell membrane. Eucaryotic cells are found in most algae, protozoa, all multicellular organisms (plants and animals) including humans. The genetic material in the nucleus forms multiple chromosomes that are linear and complexed with proteins that help the DNA 'pack' and are involved in regulation of gene expression. The cells of higher plants differ from animal cells in that 11 of 32 An animal Cell 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version they have large vacuoles, a cell wall, chloroplasts, and a lack of lysosomes, centrioles, pseudopods, and flagella or cilia. Animal cells do not have the chloroplasts, and may or may not have cilia, pseudopods or flagella, depending on the type of cell. << Prokaryotes | Eukaryotes | Plants >> Cell biology Unique Properties of Plant Cells Biology_Cell_biology | Types of cells << Eukaryotes | Unique Properties of Plant Cells Plant Cells have a number of important differences compared to their animal counterparts. The major ones are the Chloroplasts, Cell walls and Vacuoles. Unlike animal cells, plant cells do not have centrioles. Chloroplasts The chloroplasts are an organelle similar to the mitochondria in that they are self reproducing and the are energy factories of the cell. There most of the similarities ends. Chloroplasts capture light energy from the sun and convert it into ATP and sugar. In this way the cell can support itself without food. vvv Vacuoles Plants often have large structures containing water surrounded by a membrane in the centre of their cells. These are vacuoles and act as a store of water and food (in seeds), a place to dump wastes and a structural support for the cell to maintain turgor. When the plant loses water the vacuoles quickly lose their water, and when plants have a lot of water the vacuoles fill up. In mature plants there is usually one large vacuole in the centre of the cell. Cell walls Plant cells are not flaccid like animal cells and have a rigid cell wall around them made of fibrils of cellulose embedded in a matrix of several other kinds of polymers such as pectin and lignin. The cellulose molecules are linear and provide the perfect shape for intermolecular hydrogen bonding to produce long, stiff fibrils. It is the cell wall that is primarily responsible for ensuring the cell does not burst in hypertonic surroundings. This wiki is incomplete, you can help by expanding it Nucleus: Is the most important organelle in the cell. It is in here one will find the genes 12 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version in the chromosomes .The genes controls all activities that carries out by all organisms and this are passed on by the parents to their offspring to one generation to the next. Cytoplasm: This cell has a very complex structure and can only be seen under a microscope light, it consistence is a jelly like material between the outer membrane and the inner nucleus. Cell membrane: This membrane is made up of lipids or fats and proteins; it carries out the function of protection, it protects what is inside the cell from the danger that is present in the external environment. Cell wall Structure produced by some cells outside their cell membrane; variously composed of chitin, peptidoglycan, or cellulose. It is the cell wall that is primarily responsible for ensuring the cell does not burst in hypertonic surroundings. Chloroplast: This is a sack that contains pigments called chlorophyll. This subject absorbs energy from the sun which the plant cell will use to combine carbon dioxide and water to form glucose during photosynthesis. In this way the cell can support itself without food. Parts of the cell Membranes Cell biology | Parts of the cell Membranes | Organelles >> 13 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version The phospholipid bilayer which the cell membrane is an example of, is composed of various cholesterol, phospholipids, glycolipids and proteins. Below is an example of a simple phospholipid bilayer. The smaller molecules shown between the phospholipids are Cholesterol molecules. They help to provide rigidity or stability to the membrane. The two main components of phospholipids are shown in these figures by blue circles Plasma membrane bilayer representing the hydrophilic head groups and by long thin lines representing the hydrophobic fatty acid tails. Both the interior of the cell and the area surrounding the cell is made up of water or similar aqueous solution. Consequently, phospholipids orient themsleves with respect to the water and with each other so that the hydrophilic ("water loving") head groups are grouped together and face the water, and the hydrophobic ("water fearing") tails turn away from the water and toward each other. This self-organization of phospholipids results in one of just a few easily recognizable structures. Cell membranes are constructed of a phospholipid bilayer as shown above. Smaller structures can also form, known as 'micelles' in which there is no inner layer of of phospholipid. Instead, the interior of a micell is wholly hydrophobic, filled with the fatty acid chains of the phospholipids and any other hydrophobic molecule they enclose. Micelles are not so important for the understanding of cellular structure, but are useful for demonstrating the principles of hydrophilicity and hydrophobicity, and for contrasting with lipid bilayers. At least 10 different types of lipids are commonly found in cell membranes. Each type of cell or organelle will have a different percentage of each lipid, protein and carbohydrate. The main types of lipids are: Cholesterol Glycolipids Phosphatidylcholine Sphingomyelin Phosphatidylethnolamine Phosphatydilinositol 14 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Phosphatidylserine Phosphatidylglycerol Diphosphatidylglycerol (Cardiolipin) Phosphatidic acid 1. 2. 3. 4. 5. 6. Phospholipids Cholesterol Semi-permeability and Osmosis Proteins and channels Hydrophobicity Self-assembly Membranes | Organelles >> Cell biology | Parts of the cell Organelles Cell biology | Parts of the cell << Membranes | Organelles | Genetic material >> Nucleus The nucleus contains genetic material or DNA in the form of chromatin. It is a double membraned stucture, with pores on it. These pores act as a "gateway" to help the nucleoplasm to maintain continuity with the cytoplasm. The nucleus also contains the nucleolus which is responsable for the sythesis (creation) of Ribosomes. The nucleus is the "thinking" center. Mitochondria Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles A mitochondrian is the organelle responsible for a cell's metabolism. It synthetizes ATP through a protein called ATP synthase. Mitochondria have a double membrane. An outer membrane and a folded inner membrane. The internal membrane, called the cristae is invaginated (folded or creased), to maximize surface area enabling it to hold more ATP synthases. 15 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Chloroplasts Chloroplasts are found only in photosynthesizing cells; e.g. plant cells. Chloroplasts carry out photosynthesis by using several photosystem proteins. Chloroplasts also give a cell its green colour and are widely believed to have evolved from symbiotic prokaryotes that adapted to live inside eukaryotic cells. Ribosomes Ribosomes are responsible for protein synthesis; they are composed of two subunits that to elongate an aminoacid sequence. Endoplasmic Reticulum The Endoplasmic Reticulum (ER) acts as a transport from the nucleus and ribosomes to the Golgi apparatus. There are two types of endoplasmic reticulum: Smooth ER Smooth ER act as transport for various things, mainly the RNA from the nucleus to the ribosomes (RNA is a small piece of the DNA code specifically designed to tell the ribosomes what to make). Smooth ER appears smooth in texture, hence the name. Rough ER Rough ER are "rough" because of the ribosomes embedded in them. The rough ER take the protein to the Golgi apparatus to be packaged into vacuoles Golgi Complex The Golgi Complex bonds functional groups to different biomolecules to direct them to their respective destinations. It basically "packages" the stuff into vacuoles. The Golgi Complex looks like pieces of pita bread stacked on top of each other.They are the ones that have their origin from the ER.They basically function as the delivery system of the cell. Vacuole Vacuoles are storage places. They store water or cell waste products. Central Vacuole The central vacuole is found only in plant cells. It is filled with water and is pressurised, like a balloon. This forces all the other organelles within the cell out toward the cell wall. This pressure is called turgor pressure and is what gives plants their "crisp" and firm structure. 16 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Peroxisomes Peroxisomes perform a variety of metabolic processes and as a by-product, produce hydrogen peroxide. Peroxisomes use peroxase enzyme to break down this hydrogen peroxide into water and oxygen. Lysosomes Lysosomes are vacuoles containing digestive and destructive membranes. In white blood cells, these are used to kill the bacteria or virus, while in tadpole-tail cells they kill the cell by separating the tail from the main body. A day in the life of a cell The nucleus has translated a piece of its DNA, called RNA, and sent it to the ribosomes embedded in the rough endoplasmic reticulum. These ribosomes then make some valuable protein, which is then transported to the Golgi Apparatus. The Golgi Apparatus "packages" the protein into a secretory vesicle where it eventually reaches the cell membrane ready for secretion out of the cell and into the external environment. Links For more info go to http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/cells.htm << Membranes | Organelles | Genetic material >> Cell biology | Parts of the cell Genetic material Cell biology | Parts of the cell << Organelles | Genetic material | Energy supply (chloroplasts and mitochondria) >> 1. 2. 3. 4. 5. 6. 7. 8. 17 of 32 Genetic material of Prokaryotes Genetic material of Eukaryotes Nucleus Nuclear membrane Nucleolus Codons RNA polymerase Histones 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version << Organelles | Genetic material | Energy supply (chloroplasts and mitochondria) >> Cell biology | Parts of the cell Energy supply mitochondria) (chloroplasts and Cell biology | Parts of the cell << Genetic material | Energy supply (chloroplasts and mitochondria) Chloroplasts are the organelles that incorporate energy into storage while mitochondria are the ones that release the energy from the stores. Chloroplasts are flat discs usually 2-10 micrometer in diameter and 1 micrometer thick. The chloroplast has a two membrane envelope termed the Inner & Outer membrane respectively. Between these two layers is the intermembrane space. Photosynthesis 1. Light Dependent Reactions 2. Calvin-Benson Cycle The inside of a chloroplast with the granum circled. Respiration 1. Glycolysis 2. Krebs cycle 3. Electron transport << Genetic material | Energy supply (chloroplasts and mitochondria) Cell biology | Parts of the cell Cell division Cell cycle Cell biology | Cell biology:Cell division The normal cell cycle consists of 3 major stages. The first is Interphase, during which 18 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version the cell lives and grows larger. The second is Mitosis, when the cell divides. The final one is Cytokinesis, which is when the two daughter cells complete their separation. From Wikipedia The cell cycle is the cycle of a biological cell, consisting of repeated mitotic cell division and interphase (the growth phase). A cell spends the overwhelming majority of its time in the growth phases. Overview The cell cycle consists of G1 phase, the first growth phase S phase, during which the DNA is replicated, where S stands for the Synthesis of DNA. G2 phase is the second growth phase, also the preparation phase for the M phase or mitosis and cytokinesis, the actual division of the cell into two daughter cells The cell cycle stops at several checkpoints and can only proceed if certain conditions Schematic of the cell cycle. I=Interphase, M=Mitosis. are met, for example, if the The duration of mitosis in relation to the other phases has cell has reached a certain been exaggerated in this diagram. diameter. Some cells, such as neurons, never divide once they become locked in a G0 phase..........................................................v Details of mitosis 19 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Schematic of interphase (brown) and mitosis (yellow). Meiosis Cell biology | Cell biology:Cell division Meiosis is a special type of cell division that is designed to produce gametes. Like normal cell division, the cell will be double diploid and have a pair of each chromosome. Meiosis consists of 2 cell divisions, and results in four cells. The first division is when genetic crossover occurs and the traits on the chromosomes are shuffled. The cell will perform a normal prophase, then enter metaphase during which it begins the crossover, then proceed normally through anaphase and telophase. The first division produces two normal diploid cells, however the process is not complete. The cell will prepare for another division and enter a second prophase. During the second metaphase, the chromosome pairs are separated so that each new cell will get half the normal genes. The cell division will continue thorough anaphase and telophase, and the nuclei will reassemble. The result of the divisions will be 4 haploid gamete cells. From Wikipedia Crossover Crossover is the process by which two chromosomes paired up during prophase I of meiosis exchange a distal portion of their DNA. Crossover occurs when two chromosomes, normally two homologous instances of the same chromosome, break and connect to each other's ends. If they break at the same locus, this merely results in an exchange of genes. This is the normal way in which crossover occurs. If they break at different loci, the result is a duplication of genes on one chromosome and a deletion on the other. If they break on opposite sides of the centromere, this results in one chromosome being lost during cell division. Any pair of homologous chromosomes may be expected to cross over three or four times during meiosis. This aids evolution by increasing independent assortment, and reducing the genetic linkage between genes on the same chromosome. 20 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Mitosis Cell biology | Cell biology:Cell division Mitosis is the normal type of cell division. Before the cells can divide, the chromosomes will have duplicated and the cell will have twice the normal set of genes. The first step of cell division is prophase, during which the nucleus dissolves and the chromosomes begin migration to the midline of the cell. (Some biology textbooks insert a phase called "prometaphase" at this point.)The second step, known as metaphase, occurs when all the chromosomes are aligned in pairs along the midline of the cell. As the cell enters anaphase, the chromatids, which form the chromosomes, will separate and drift toward opposite poles of the cell. As the separated chromatids, now termed chromosomes, reach the poles, the cell will enter telophase and nuclei will start to reform. The process of mitosis ends after the nuclei have reformed and the cell membrane begins to separate the cell into two daughter cells, during cytokinesis. From Wikipedia In biology, Mitosis is the process of chromosome segregation and nuclear division that follows replication of the genetic material in eukaryotic cells. This process assures that each daughter nucleus receives a complete Mitosis divides genetic information during cell division. copy of the organism's genetic material. In most eukaryotes, mitosis is accompanied with cell division or cytokinesis, but there are many exceptions, for instance among fungi. There is another process called meiosis, in which the daughter nuclei receive half the chromosomes of the parent, which is involved in gamete formation and other similar processes. Mitosis is divided into several stages, with the remainder of the cell's growth cycle considered interphase. Properly speaking, a typical cell cycle involves a series of stages: G1, the first growth phase; S, where the genetic material is duplicated; G2, the second growth phase; and M, where the nucleus divides through mitosis. Mitosis is divided into prophase, prometaphase, metaphase, anaphase and telophase. The whole procedure is very similar among most eukaryotes, with only minor variations. As prokaryotes lack a nucleus and only have a single chromosome with no centromere, they cannot be properly said to undergo mitosis. Prophase 21 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version The genetic material (DNA), which normally exists in the form of chromatin condenses into a highly ordered structure called a chromosome. Since the genetic material has been duplicated, there are two identical copies of each chromosome in the cell. Identical chromosomes (called sister chromosomes) are attached to each other at a DNA element present on every chromosome called the centromere. When chromosomes are paired up and attached, each individual chromosome in the pair is called a chromatid, while the whole unit (confusingly) is called a chromosome. Just to be even more confusing, when the chromatids separate, they are no longer called chromatids, but are called chromosomes again. The task of mitosis is to assure that one copy of each sister chromatid - and only one copy - goes to each daughter cell after cell division. Prophase: The two round objects above the nucleus are the centrosomes. Note the condensed chromatin. The other important piece of hardware in mitosis is the centriole, which serves as a sort of anchor. During prophase, the two centrioles - which replicate independently of mitosis - begin recruiting microtubules (which may be thought of as cellular ropes or poles) and forming a mitotic spindle between them. By increasing the length of the spindle (growing the microtubules), the centrioles push apart to opposite ends of the cell nucleus. It should be noted that many eukaryotes, for instance plants, lack centrioles although the basic process is still similar. Prometaphase Some biology texts do not include this phase, considering it a part of prophase. In this phase, the nuclear membrane dissolves in some eukaryotes, reforming later once mitosis is complete. This is called open mitosis, found in most multicellular forms. Many protists undergo closed mitosis, in which the nuclear membrane persists throughout. Now kinetochores begin to form at the centromeres. This is a complex structure that may be thought of as an 'eyelet' for the microtubule 'rope' - it is the attaching point by which chromosomes may be secured. The kinetochore is an enormously complex structure that is not yet fully understood. Two kinetochores form on each chromosome - one for each chromatid. When the spindle grows to sufficient length, the microtubules begin searching for kinetochores to attach to. Metaphase 22 of 32 Prometaphase: The nuclear membrane has degraded, and microtubules have invaded the nuclear space. These microtubules can attach to kinetochores or they can interact with opposing microtubules. 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version As microtubules find and attach to kinetochores, they begin to line up in the middle of the cell. Proper segragation requires that every kinetochore be attached to a microtubule before separation begins. It is thought that unattached kinetochores control this process by generating a signal - the mitotic spindle checkpoint - that tells the cell to wait before proceeding to anaphase. There are many theories as to how this is accomplished, some of them involving the generation of tension when both microtubules are attached to the kinetochore. Metaphase: The chromosomes have aligned at the metaphase plate. When chromosomes are bivalently attached - when both kinetochores are attached to microtubules emanating from each centriole - they line up in the middle of the spindle, forming what is called the metaphase plate. This does not occur in every organism - in some cases chromosomes move back and forth between the centrioles randomly, only roughly lining up along the midline. Anaphase Anaphase is the stage of meiosis or mitosis when chromosomes separate and move to opposite poles of the cell (opposite ends of the nuclear spindle). Centromeres are broken and chromatids rip apart. When every kinetochore is attached to a microtubule and the chromosomes have lined up along the middle of the spindle, the cell proceeds to anaphase. This is divided into two phases. First, the proteins that bind the sister chromatids together are cloven, allowing them to separate. They are pulled apart by the microtubules, towards the respective centrioles to which they are attached. Next, the spindle axis elongates, driving the centrioles (and the set of chromosomes to which they are attached) apart to opposite ends of the cell. These two stages are sometimes called 'early' and 'late' anaphase. Early anaphase: Kinetochore microtubules shorten At the end of anaphase, the cell has succeeded in separating identical copies of the genetic material into two distinct populations. Telophase 23 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version Now the nuclear membrane reforms around the genetic material and the chromosomes are unfolded back into chromatin. This is often followed by cytokinesis or cleavage, where the cellular membrane pinches off between the two newly separated nuclei, to form two new daughter cells. Cytokinesis Cytokinesis refers to the physical division of one eukaryotic cell. Cytokinesis generally follows the replication of the cell's Telophase: The pinching is chromosomes, usually mitotically, but sometimes known as the cleavage meiotically. Except for some special cases, the amount of furrow. Note the decondensing chromosomes. cytoplasm in each daughter cell is the same. In animal cells, the cell membrane forms a cleavage furrow and pinches apart like a balloon. In plant cells, a cell plate forms, which becomes the new cell wall separating the daughters. Various patterns occur in other groups. Genes Expression Gene expression is the first stage of a process that decodes what the DNA holds in a cell. It is the expression of a gene that gives rise to a protein. How does gene expression occur? It starts of with transcription that gives rise to the middlemen namely the RNA. The RNA relay information from the chromosomal DNA to the cytoplasm where the machinary for protein synthesis resides. Translation occurs following transcription wherein the protein synthesis machinary gets into action and uses its tools to read out the message that the RNA holds. The details of this process are indeed very complex and will probably be dealt with in an advanced writeup. Translation Note:This book needs to be de-wikified. Keep in mind that most Wikibooks modules use inter-wiki linking generally done much less than a typical Wikipedia article, and terms that are critical to understanding the module. This means most of the links can simply be removed altogether if content Wikipedia during a transwiki move. 24 of 32 rather sparsely, and is only to reference key that for the most part has been copied from 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version It is very seldom that you will find a Wikibook using a common word by itself, which is also why most of the imported articles from Wikipedia are full of red links. It would be better if you simply removed the red links altogether in most cases. If you insist on keeping some or all of the links, please make sure that especially the red links have been changed with a "wikipedia" prefix, such as [[wikipedia:Color|]] or use the "w" abbrivation of [[w:Color|]]. Both are valid inter-wiki links on all Wikimedia projects. The Translation Phase of Genetic Expression is divided into 2 Steps Transcription and Translation. During Transcription RNA Polymerase unzips the two halfs of the DNA where it needs to transcript. Then free RNA bases Attach to the DNA bases with the Polymerase starting at the promoter and ending at the Termination signal. From this the RNA can become mRNA, rRNA, or tRNA. The mRNA is a ribbon like strand that takes the genetic information from the nucleus of the cell to the ribosome. rRNA forms a globular ball that attaches to the rough E.R. to help make ribosomes. finally the tRNA forms a hair shaped landing base that reads the genetic information to make proteins. Translation happens when mRNA is pulled through a ribosome and tRNA reads the RNA bases on the mRNA to make anti-codons of 3 bases and brings amino-acids to form the protein. This starts with the condon AUG and ends at UAG. When done the protein forms the correct shape and does the task it was created for. This brings the genetic code from the nucleus, which it never leaves, to the cytoplasm of the cell where proteins are produced to upkeep the body. License GNU Free Documentation License Version 1.2, November 2002 Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. 0. PREAMBLE The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others. 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If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. Retrieved from "http://en.wikibooks.org/wiki/Cell_Biology/Print_version" Categories: Books with print version | Biology | Cell Biology | Modules that need to be wikified 31 of 32 23/11/06 15:03 Cell Biology/Print version - Wikibooks, collection of open-content t... http://en.wikibooks.org/wiki/Cell_Biology/Print_version This page was last modified 08:47, 17 November 2006. All text is available under the terms of the GNU Free Documentation License (see Copyrights for details). Wikibooks® is a registered trademark of the Wikimedia Foundation, Inc. Privacy policy About Wikibooks Disclaimers 32 of 32 23/11/06 15:03 Reading(s) #1.3 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... On-Line Biology Book: GLOSSARY PQ pacemaker. See sinoatrial node. Pacinian corpuscles Sensory receptors located deep in the epidermis that detect pressure and vibration. paleontology The study of ancient life by collection and analysis of fossils. Paleozoic Era The period of time beginning 570 million years ago ending 245 million years ago; falls between the Proterozoic and Mesozoic Eras and is divided into the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian Periods. PICTURE palindrome A sequence that reads the same in either direction; in genetics, refers to an enzyme recognition sequence that reads the same on both strands of DNA. palisade Layer of mesophyll cells in leaves that are closely placed together under the epidermal layer of the leaf. Palisade parenchyma: Columnar cells located just below the upper epidermis in leaves the cells where most of the light absorbtion in photosynthesis occurs. PICTURE 1 | PICTURE 2 palynology The study of palynomorphs and other acid-resistant microfossils usually produced by plants, protists, and fungi palynomorph Generic term for any object a palynologist studies. pancreas A gland in the abdominal cavity that secretes digestive enzymes into the small intestine and also secretes the hormones insulin and glucagon into the blood, where they regulate blood glucose levels. A digestive organ that produces trypsin, chymotrypsin and other enzymes as a pancreatic juice, but which also has endocrine functions in the production of the hormones somatostatin, insulin, and glucagon. pancreatic islets Clusters of endocrine cells in the pancreas that secrete insulin and glucagon; also known as islets of Langerhans. Pangaea The name proposed by German meteorologist Alfred Wegener for a supercontinent that existed at the end of the Paleozoic Era and consisted of all the Earth's landmasses. parallel evolution The development of similar characteristics in organisms that are not closely related (not part of a monophyletic group) due to adaptation to similar environments and/or strategies of life. parasites Organisms that live in, with, or on another organism. The parasites beneÞt 1 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... from the association without contributing to the host, usually they cause some harm to the host. parasitism A form of symbiosis in which the population of one species beneÞts at the expense of the population of another species; similar to predation, but differs in that parasites act more slowly than predators and do not always kill the host. A type of symbiosis in which one organism benefits at the expense of the other, for example the influenza virus is a parasite on its human host. Viruses, are obligate intracellular parasites. parasympathetic system The subdivision of the autonomic nervous system that reverses the effects of the sympathetic nervous system. Part of the autonomic nervous system that controls heartbeat, respiration and other vital functions. parenchyma One of the three major cell types in plants. Parenchyma cells have thin, usually multisided walls, are unspecialized but carry on photosynthesis and cellular respiration and can store food; form the bulk of the plant body; found in the þeshy tissue of fruits and seeds, photosynthetic cells of leaves, and the vascular system. Generalized plant cells whose numerous functions include photosynthesis, storage, bulk of herbaceous stem tissues, lateral transport in woody stems. Parenchyma are variously shaped but are characterized by thin walls and remain alive at functional maturity. PICTURE parietal lobe The lobe of the cerebral cortex that lies at the top of the brain; processes information about touch, taste, pressure, pain, and heat and cold. PICTURE passive transport Diffusion across a plasma membrane in which the cell expends no energy. pectin A substance in the middle lamella that cements adjoining plant cells together. pectoral girdle In humans, the bony arch by which the arms are attached to the rest of the skeleton; composed of the clavicle and scapula. PICTURE pedigree analysis A type of genetic analysis in which a trait is traced through several generations of a family to determine how the trait is inherited. The information is displayed in a pedigree chart using standard symbols. pelagic zone One of the two basic subdivisions of the marine biome; consists of the water above the sea þoor and its organisms. pelvic girdle In humans, the bony arch by which the legs are attached to the rest of the skeleton; composed of the two hipbones. PICTURE pelvis The hollow cavity formed by the two hipbones. PICTURE penicillin The first of the so-called wonder drugs; discovered by Sir Alexander Fleming. 2 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... pepsin An enzyme produced from pepsinogen that initiates protein digestion by breaking down protein into large peptide fragments. An enzyme, produced by the stomach, that chemically breaks down peptide bonds in polypeptides and proteins. pepsinogen An inactive form of pepsin; synthesized and stored in cells lining the gastric pits of the stomach. peptic ulcer Damage to the epithelial layer of the stomach lining; generally caused by bacterial infection. peptide bond A covalent bond that links two amino acids together to form a polypeptide chain. A covalent bond between the amine end of one amino acid and the acid end of another amino acid. PICTURE peptides Short chains of amino acids. perichondrium A layer of connective tissue that forms around the cartilage during bone formation. Cells in the perichondrium lay down a peripheral layer that develops into compact bone. perennials Plants that persist in the environment for more than one year (as in the case of annuals). period The fundamental unit in the hierarchy of time units; a part of geologic time during which a particular sequence of rocks designated as a system was deposited. Units of geological time that are the major subdivisions of Eras. periosteum A Þbrous membrane that covers bones and serves as the site of attachment for skeletal muscles; contains nerves, blood vessels, and lymphatic vessels. peripheral nervous system The division of the nervous system that connects the central nervous system to other parts of the body. Components of the nervous system that transmit messages to the central nervous system. peristalsis Involuntary contractions of the smooth muscles in the walls of the esophagus, stomach, and intestines that propel food along the digestive tract. Waves of muscle contraction in the esophagus that propel food from the oral cavity to the stomach. PICTURE Permian Period The last geologic time period of the Paleozoic Era, noted for the greatest mass extinction in earth history, when nearly 96% of species died out. PICTURE peroxisomes Membrane-bound vesicles in eukaryotic cells that contain oxidative enzymes. pesticides Chemicals that are applied to agricultural crops or domesticated plants and which kill or inhibit growth of insects. 3 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... petals Usually brightly colored elements of a þower that may produce fragrant oils; nonreproductive structures that attract pollinators. Sterile leaf-like (white, colorless, but usually colored) structures in flowers that serve to attract pollinators. PICTURE petiole The generally non-leafy part of the leaf that attaches the leaf blade to the stem; celery and rhubarb are examples of a leaf petiole that we use as food. The stalk connecting the leaf blade to the stem. PICTURE PGA (phosphoglycerate) A three-carbon molecule formed when carbon dioxide is added to ribulose biphosphate (RuBP) during the dark reaction of photosynthesis (Calvin, or Calvin-Benson Cycle). PGA is converted to PGAL, using ATP and NADPH. PGAL (phosphoglyceraldehyde) A substance formed from PGA during the dark reaction of photosynthesis. Some PGAL leaves the cycle and can be converted to glucose, while other PGAL molecules are used to reform ribulose biphosphate (RuBP) to continue the dark reaction. pH The negative logarithm of the H+ ion concentration. The pH is a measure of the acidity or basic character of a solution. Since it measures a fraction, the larger the pH number, the less H ions are present in a solution. PICTURE phagocytes White blood cells that can engulf (by phagocytosis) and destroy microorganisms including viruses and bacteria; cells in this category include neutrophils and monocytes. phagocytosis A form of endocytosis in which white blood cells surround and engulf invading bacteria or viruses. PICTURE pharynx The passageway between the mouth and the esophagus and trachea. Food passes from the pharynx to the esophagus, and air passes from the pharynx to the trachea. phenotype The observed properties or outward appearance of a trait. The physical expression of the alleles posessed by an organism. pheromones Chemical signals that travel between organisms rather than between cells within an organism; serve as a form of communication between animals. phloem Tissue in the vascular system of plants that moves dissolved sugars and other products of photosynthesis from the leaves to other regions of the plant. Phloem tissue consists of cells called sieve tubes and companion cells. Cells of the vascular system in plants that transport food from leaves to other areas of the plant. PICTURE 1 | PICTURE 2 | PICTURE 3 phosphate group A chemical group composed of a central phosphorous bonded to three or four oxygens. The net charge on the group is negative. PICTURE 4 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... phospholipids Asymmetrical lipid molecules with a hydrophilic head and a hydrophobic tail. Lipids with a phosphate group in place of one of the three fatty acid chains. Phospholipids are the building blocks of cellular membranes. Phospholipids have hydrophilic heads (glycerol and phosphate) and hydrophobic tails (the non-polar fatty acids). PICTURE phosphorylation The chemical attachment of phosphorous to a molecule, usually associated with the storage of energy in the covalent bond that is also formed. Example: attachment of the third phosphate group to ADP in the formation of the higher energy form, ATP. Photophosphorylation is a type of phosphorylation associated with the formation of ATP in the photosynthesis process. photic zone The layer of the ocean that is penetrated by sunlight; extends to a depth of about 200 meters. photoperiodism The ability of certain plants to sense the relative amounts of light and dark in a 24-hour period; controls the onset of þowering in many plants. photosynthesis The process by which plant cells use solar energy to produce ATP. The conversion of unusable sunlight energy into usable chemical energy, associated with the actions of chlorophyll. PICTURE photosystems Clusters of several hundred molecules of chlorophyll in a thylakoid in which photosynthesis takes place. Eukaryotes have two types of photosystems: I and II. The series of green photoreceptive pigments involved in the light reactions, which occur in the thylakoids of the chloroplast (in eukaryotes). Energy from light is passed to the electrons as they move through the photosystem pigments. PICTURE 1 | PICTURE 2 | PICTURE 3 | PICTURE 4 phototrophs Organisms that use sunlight to synthesize organic nutrients as their energy source; e.g., cyanobacteria, algae, and plants. phototropism The reaction of plants to light in which the plants bend toward the light. Plant response to light by unequal growth caused by concentration of the plant hormone Indole Acetic Acid (IAA, an auxin) on the darker side of the plant shoot. PICTURE phycocyanin An accessory pigment found in cyanobacteria and the chloroplasts of red algae. phycoerythrin An accessory pigment found in cyanobacteria and the chloroplasts of red algae. phylogeny 1) the study of evolutionary relationships within a monophyletic group. 2) evolutionary hypotheses represented as a dendrogram or branching diagram. PICTURE 1 | PICTURE 2 phylogenetic Pertaining to a phylogeny. 5 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... phylum The broadest taxonomic category within kingdoms (pl.: phyla). PICTURE phytochrome A pigment in plant leaves that detects day length and generates a response; partly responsible for photoperiodism. phytoplankton A þoating layer of photosynthetic organisms, including algae, that are an important source of atmospheric oxygen and form the base of the aquatic food chain. pilus Projection from surface of a bacterial cell (F+) that can donate genetic material to another (F-). pineal gland A small gland located between the cerebral hemispheres of the brain that secretes melatonin. pioneer community The initial community of colonizing species. pistil Female reproductive structures in flowers, consisting of the stigma, style, and ovary. Also known as a carpel in some books. PICTURE 1 | PICTURE 2 pith Central area in plant stems, largely composed of parenchyma tissue modified for storage. PICTURE 1 | PICTURE 2 pituitary gland A small gland located at the base of the brain; consists of an anterior and a posterior lobe and produces numerous hormones. The master gland of the endocrine system, the pituitary releases hormones that have specific targets as well as those that stimulate other glands to secrete hormones. Part of the pituitary is nerve tissue, the rest is glandular epithelium. PICTURE 1 | PICTURE 2 placenta An organ produced from interlocking maternal and embryonic tissue in placental mammals; supplies nutrients to the embryo and fetus and removes wastes. placental mammals One of three groups of mammals that carry their young in the mother's body for long periods during which the fetus is nourished by the placenta. Humans are placental mammals. planaria Small free-living þatworms (Phylum Platyhelminthes) with bilateral symmetry and cephalization. The freshwater type is often used as an experimental organism. planktonic organisms "Floaters"; one of the two main types of organisms in the pelagic zone of the marine biome. Plantae The plant kingdom; nonmobile, autotrophic, multicellular eukaryotes. Kingdom of the plants, autotrophic eukaryotes with cellulose in their cell walls and starch as a carbohydrate storage product, with chlorophylls a and b as photosynthesis pigments. PICTURE plasma The liquid portion of the blood. Along with the extracellular þuid, it makes 6 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... up the internal environment of multicellular organisms. plasma cells Cells produced from B cells that synthesize and release antibodies. PICTURE plasmids Self-replicating, circular DNA molecules found in bacterial cells; often used as vectors in recombinant DNA technology. Small circles of double-stranded DNA found in some bacteria. Plasmids can carry from four to 20 genes. Plasmids are a commonly used vector in recombinant DNA studies. PICTURE plasmodesmata Junctions in plants that penetrate cell walls and plasma membranes, allowing direct communication between the cytoplasm of adjacent cells (sing.: plasmodesma). plasmolysis Osmotic condition in which a cell loses water to its outside environment. plastids Membrane-bound organelles in plant cells that function in storage (of food or pigments) or food production. Term for any double membrane-bound organelle. Chloroplasts contain the chemicals for photosynthesis, amyloplasts (also known as leukoplasts) store starch, chromoplasts contain colorful pigments such as in the petals of a flower or epidermis of a fruit. platelets In vertebrates, cell fragments that bud off from the megakaryocytes in the bone marrow; carry chemicals needed for blood clotting. Cell fragment functioning in blood clotting. plate tectonics The movement of the plates that make up the surface of the Earth. The revolutionary paradigm in geology that the earth's crust is composed of rigid segments (plates) in constant (although considered slow in a human-scale time frame) motion (tectonics) relative to each other. pleiotropic A term describing a genotype with multiple phenotypic effects. For example: sickle-cell anemia produces a multitude of consequences in those it affects, such as heart disease, jidney problem, etc. Pleistocene The first geologic epoch of the Quaternary Period of the Cenozoic Era that ended 10,000 years ago with the retreat of the last glaciers. PICTURE pleura A thin sheet of epithelium that covers the inside of the thoracic cavity and the outer surface of the lungs. pleural cavity The space between the sheets of pleura (one covering the inside of the thoracic cavity, the other covering the outside of the lungs). polar covalent bond A covalent bond in which atoms share electrons in an unequal fashion. The resulting molecule has regions with positive and negative charges. The presence of polar covalent bonds allows other polar molecules to surround molecule: example: glucose sugar in water. 7 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... pollen grains The containers for male gametophytes of seed plants produced in a microsporangium by meiosis. Microspores produced by seed plants that contain the male gametophyte. PICTURE pollen tube Structure produced by the tube nucleus in the pollen grain through which the sperm nucleus (or nuclei in angiosperms) proceed to travel through to reach the egg. PICTURE pollination The transfer of pollen from the anthers to the stigma by a pollinating agent such as wind, insects, birds, bats, or in a few cases the opening of the flower itself. polygenic inheritance Occurs when a trait is controlled by several gene pairs; usually results in continuous variation. PICTURE polymer Organic molecule composed of smaller units known as monomers. A large molecule composed of smaller subunits, for example starch is a polymer of glucose, proteins are polymers of amino acids. polymerase chain reaction (PCR) A method of amplifying or copying DNA fragments that is faster than cloning. The fragments are combined with DNA polymerase, nucleotides, and other components to form a mixture in which the DNA is cyclically amplified. polynucleotides Long chains of nucleotides formed by chemical links between the sugar and phosphate groups. polyp The sessile form of life history in cnidarians; e.g., the freshwater hydra. polyploidy Abnormal variation in the number of chromosome sets. The condition when a cell or organism has more than the customary two sets of chromosomes. This is an especially effective speciation mechanism in plants since the extra chromosomes will establish reproductive isolation with the parental population(s), an essential for speciation. PICTURE 1 | PICTURE 2 polysaccharides Long chains of monosaccharide units bonded together; e.g., glycogen, starch, and cellulose. PICTURE pons The region that, with the medulla oblongata, makes up the hindbrain, which controls heart rate, constriction and dilation of blood vessels, respiration, and digestion. PICTURE population A group of individuals of the same species living in the same area at the same time and sharing a common gene pool. A group of potentially interbreeding organisms in a geographic area. population dynamics The study of the factors that affect the growth, stability, and decline of populations, as well as the interactions of those factors. 8 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... portal system An arrangement in which capillaries drain into a vein that opens into another capillary network. positive feedback Biochemical control where the accumulation of the product stimulates production of an enzyme responsible for that product's production. positive feedback control Occurs when information produced by the feedback increases and accelerates the response. precambrian Informal term describing 7/8 of geologic time from the beginning of the earth to the beginning of the Cambrian Period of the Paleozoic Era. During this time the atmosphere and oceans formed, life originated (or possibly "colonized" Earth), eukaryotes and simple animals evolved and by the end of the precambrian they began to accumulate hard preservable parts, the common occurrence of which marks the beginning of the Cambrian. PICTURE precipitation The part of the hydrologic cycle in which the water vapor in the atmosphere falls to Earth as rain or snow. predation One of the biological interactions that can limit population growth; occurs when organisms kill and consume other living organisms. predatory release Occurs when a predator species is removed from a prey species such as by great reduction in the predator's population size or by the migration of the prey species to an area without major predators. The removal of the predator releases the prey from one of the factors limiting its population size. prehensile movement The ability to seize or grasp. prenatal testing Testing to detect the presence of a genetic disorder in an embryo or fetus; commonly done by amniocentesis or chorionic villi sampling. presymptomatic screening Testing to detect genetic disorders that only become apparent later in life. The tests are done before the condition actually appears, such as with Huntington disease. prey switching The tendency of predators to switch to a more readily available prey when one prey species becomes rare; allows the Þrst prey population to rebound and helps prevent its extinction. primary cell wall The cell wall outside the plasma membrane that surrounds plant cells; composed of the polysaccharide cellulose. primary body Those parts of a plant produced by the shoot and root apical meristems. primary compounds Chemicals made by plants and needed for the plant's own metabolism. 9 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... primary growth Cells produced by an apical meristem. The growth a plant by the actions of apical meristems on the shoot and root apices in producing plant primary tisues. primary macronutrients Elements that plants require in relatively large quantities: nitrogen, phosphorus, and potassium. primary meristems The apical meristems on the shoot and root apices in plants that produce plant primary tissues. primary root The Þrst root formed by a plant. primary structure The sequence of amino acids in a protein. PICTURE primates The taxonomic order of mammals that includes prosimians (lemurs and tarsiers), monkeys, apes, and humans; characteristics include large brain, stereoscopic vision, and grasping hand. principle of independent assortment Mendel's second law; holds that during gamete formation, alleles in one gene pair segregate into gametes independently of the alleles of other gene pairs. As a result, if enough gametes are produced, the collective group of gametes will contain all combinations of alleles possible for that organism. principle of segregation Mendel's Þrst law; holds that each pair of factors of heredity separate during gamete formation so that each gamete receives one member of a pair. prions Infectious agents composed only of one or more protein molecules without any accompanying genetic information. producers The Þrst level in a food pyramid; consist of organisms that generate the food used by all other organisms in the ecosystem; usually consist of plants making food by photosynthesis. progesterone One of the two female reproductive hormones secreted by the ovaries. prokaryote Type of cell that lacks a membrane-bound nucleus and has no membrane organelles; a bacterium. Prokaryotes are more primitive than eukaryotes. Cells lacking membrane-bound organelles and having a single circular chromosome, and ribosomes surrounded by a cell membrane. Prokaryotes were the first forms of life on earth, evolving over 3.5 billion years ago. prolactin A hormone produced by the anterior pituitary; secreted at the end of pregnancy when it activates milk production by the mammary glands. promoter The speciÞc nucleotide sequence in DNA that marks the beginning of a gene. PICTURE prophase 1) The Þrst stage of mitosis during which chromosomes condense, the nuclear envelope disappears, and the centrioles divide and migrate to opposite ends of 10 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... the cell. 2) The first stage of mitosis and meiosis (although in meiosis this phase is denoted with either a roman numeral I or II) where the chromatin condenses to form chromosomes, nucleolus dissolves, nuclear envelope dissolves, and the spindle begins to form. PICTURE prostaglandins A class of fatty acids that has many of the properties of hormones; synthesized and secreted by many body tissues and have a variety of effects on nearby cells. prostate gland A gland that is located near and empties into the urethra; produces a secretion that enhances sperm viability. Gland involved in the reproductive system in males, the prostate secretes a sperm activating chemical into the semen during the arousal/ejaculation response. PICTURE proteinoids Polymers of amino acids formed spontaneously from inorganic molecules; have enzyme-like properties and can catalyze chemical reactions. proteins Polymers made up of amino acids that perform a wide variety of cellular functions. One of the classes of organic macromolecules that function as structural and control elements in living systems. Proteins are polymers of amino acids linked together by peptide bonds. prothallus In ferns, a small heart-shaped bisexual gametophyte. PICTURE Protista The taxonomic Kingdom from which the other three eukaryotic kingdoms (Fungi, Animalia and Plantae) are thought to have evolved. The earliest eukaryotes were single-celled organisms that would today be placed in this admittedly not monophyletic group. The endosymbiosis theory suggests that eukaryotes may have evolved independently several times. protists Single-celled organisms; a type of eukaryote. Protista proton A subatomic particle in the nucleus of an atom that carries a positive charge. The positively charged (+1) subatomic particle located in the atomic nucleus and having a mass slightly less than that of a neutron. Elements differ by the number of protons in their atoms. protostomes Animals in which the Þrst opening that appears in the embryo becomes the mouth; e.g., mollusks, annelids, and arthropods. protozoa Single-celled protists grouped by their method of locomotion. This group includes Paramecium, Amoeba, and many other commonly observed protists. PICTURE 1 | PICTURE 2 proximal tubule The winding section of the renal tubule where most reabsorption of water, sodium, amino acids, and sugar takes place. PICTURE pseudocoelom In nematodes, a closed þuid-containing cavity that acts as a hydrostatic skeleton to maintain body shape, circulate nutrients, and hold the major body organs. 11 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... pseudocoelomates Animals that have a body cavity that is in direct contact with the outer muscular layer of the body and does not arise by splitting of the mesoderm; e.g., roundworms. pseudopodia Temporary cytoplasmic extensions from a cell that enables it to move (sing.: pseudopodium). PICTURE pulmonary artery The artery that carries blood from the right ventricle of the vertebrate heart to the lungs. Artery carrying oxygen-poor blood from the heart to the lungs. PICTURE pulmonary circuit The loop of the circulatory system that carries blood to and from the lungs. PICTURE pulmonary vein The vein that carries oxygenated blood from the lungs to the left atrium of the heart. Veins carrying oxygenated blood from the lungs to the heart. PICTURE punctuated equilibrium A model that holds that the evolutionary process is characterized by long periods with little or no change interspersed with short periods of rapid speciation. purine One of the groups of nitrogenous bases that are part of a nucleotide. Purines are adenine and guanine, and are double-ring structures. PICTURE pyloric sphincter The ring of muscle at the junction of the stomach and small intestine that regulates the movement of food into the small intestine. PICTURE pyrimidine One of the groups of nitrogenous bases that are part of a nucleotide. Pyrimidines are single ringed, and consist of the bases thymine (in DNA), uracil (replacing thymine in RNA), and cytosine. PICTURE quantum models of speciation Models of evolution that hold that speciation sometimes occurs rapidly as well as over long periods, as the classical theory proposed. Quaternary Period The most recent geologic period of the Cenozoic Era, the Quaternary began 2 million years ago with the growth of northern hemisphere continental glaciers and the ice age. PICTURE quaternary structure In some proteins, a fourth structural level created by interactions with other proteins. Aspect of protein structure determined by the number and arrangement of polypeptides in a large protein such as hemoglobin. PICTURE Text ©1992, 1994, 1995, 1997, 1998, 1999, 2000, M.J. Farabee, all rights reserved. Back to Table of Contents | Back to Main Glossary Page 12 of 13 23/11/06 15:04 GLOSSARY PQ http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgloss... Email: mj.farabee@emcmail.maricopa.edu Last modified: The URL of this page is: 13 of 13 23/11/06 15:04 Reading(s) #1.4 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... CELLS II: CELLULAR ORGANIZATION Table of Contents Cell Size and Shape | The Cell Membrane | The Cell Wall | The Nucleus | Cytoplasm | Vacuoles and Vesicles | Ribosomes Endoplasmic Reticulum | Golgi Apparatus and Dictyosomes | Lysosomes | Mitochondria | Plastids | Cell Movement Learning Objectives | Terms | Review Questions | Links | References According to the Cell Theory, all living things are composed of one or more cells. Cells fall into prokaryotic and eukaryotic types. Prokaryotic cells are smaller (as a general rule) and lack much of the internal compartmentalization and complexity of eukaryotic cells. No matter which type of cell we are considering, all cells have certain features in common: cell membrane, DNA, cytoplasm, and ribosomes. Cell Size and Shape | Back to Top The shapes of cells are quite varied with some, such as neurons, being longer than they are wide and others, such as parenchyma (a common type of plant cell) and erythrocytes (red blood cells) being equidimensional. Some cells are encased in a rigid wall, which constrains their shape, while others have a flexible cell membrane (and no rigid cell wall). The size of cells is also related to their functions. Eggs (or to use the latin word, ova) are very large, often being the largest cells an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg (now termed a zygote) are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy that is available in the zygote cells. Later in life the energy must be acquired, but at first a sort of inheritance/trust fund of energy is used. 1 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION 2 of 25 http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Sizes of viruses, cells, and organisms. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. The Cell Membrane | Back to Top The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. This layering is termed a bilayer since an electron microscopic technique known as freeze-fracturing is able to split the bilayer. Diagram representing the cell membrane. The above image is from http://www.biosci.uga.edu/almanac/bio_103/notes/may_15.html. 3 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Cell Membranes from Opposing Neurons (TEM x436,740). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Cholesterol is another important component of cell membranes embedded in the hydrophobic areas of the inner (tail-tail) region. Most bacterial cell membranes do not contain cholesterol. Proteins are suspended in the inner layer, although the more hydrophilic areas of these proteins "stick out" into the cells interior and outside of the cell. These proteins function as gateways that will, in exchange for a price, allow certain molecules to cross into and out of the cell. These integral proteins are sometimes known as gateway proteins. The outer surface of the membrane will tend to be rich in glycolipids, which have their hydrophobic tails embedded in the hydrophobic region of the membrane and their heads exposed outside the cell. These, along with carbohydrates attached to the integral proteins, are thought to function in the recognition of self. The contents (both chemical and organelles)of the cell are termed protoplasm, and are further subdivided into cytoplasm (all of the protoplasm except the contents of the nucleus) and nucleoplasm (all of the material, plasma and DNA etc. within the nucleus). The Cell Wall | Back to Top Not all living things have cell walls, most notably animals and many of the more animal-like Protistans. Bacteria have cell walls containing peptidoglycan. Plant cells 4 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... have a variety of chemicals incorporated in their cell walls. Cellulose is the most common chemical in the plant primary cell wall. Some plant cells also have lignin and other chemicals embedded in their secondary walls. The cell wall is located outside the plasma membrane. Plasmodesmata are connections through which cells communicate chemically with each other through their thick walls. Fungi and many protists have cell walls although they do not contain cellulose, rather a variety of chemicals (chitin for fungi). Structure of a typical plant cell. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 5 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Lily Parenchyma Cell (cross-section) (TEM x7,210). Note the large nucleus and nucleolus in the center of the cell, mitochondria and plastids in the cytoplasm. This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Structure of an animal cell. The above image is from http://www.biosci.uga.edu/almanac/bio_103/notes/may_15.html. 6 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Liver Cell (TEM x9,400). This image is copyright Dennis Kunkel This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. The nucleus | Back to Top The nucleus occurs only in eukaryotic cells, and is the location of the majority of different types of nucleic acids. Van Hammerling's experiment (click here for a diagram) showed the role of the nucleus in controlling the shape and features of the cell. Deoxyribonucleic acid, DNA, is the physical carrier of inheritance and with the exception of plastid DNA (cpDNA and mDNA, see below) all DNA is restricted to the nucleus. Ribonucleic acid, RNA, is formed in the nucleus by coding off of the DNA bases. RNA moves out into the cytoplasm. The nucleolus is an area of the nucleus (usually 2 nucleoli per nucleus) where ribosomes are constructed. 7 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Structure of the nucleus. Note the chromatin, uncoiled DNA that occupies the space within the nuclear envelope. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Liver cell nucleus and nucleolus (TEM x20,740). Cytoplasm, mitochondria, endoplasmic reticulum, and ribosomes also shown.This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. 8 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... The nuclear envelope is a double-membrane structure. Numerous pores occur in the envelope, allowing RNA and other chemicals to pass, but the DNA not to pass. Structure of the nuclear envelope and nuclear pores. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Nucleus with Nuclear Pores (TEM x73,200). The cytoplasm also contains numerous ribosomes. This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. 9 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Cytoplasm | Back to Top The cytoplasm was defined earlier as the material between the plasma membrane (cell membrane) and the nuclear envelope. Fibrous proteins that occur in the cytoplasm, referred to as the cytoskeleton maintain the shape of the cell as well as anchoring organelles, moving the cell and controlling internal movement of structures. Microtubules function in cell division and serve as a "temporary scaffolding" for other organelles. Actin filaments are thin threads that function in cell division and cell motility. Intermediate filaments are between the size of the microtubules and the actin filaments. Actin and tubulin components of the cytoskeleton. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Vacuoles and vesicles | Back to Top Vacuoles are single-membrane organelles that are essentially part of the outside that is located within the cell. The single membrane is known in plant cells as a tonoplast. Many organisms will use vacuoles as storage areas. Vesicles; are much smaller than vacuoles and function in transport within and to the outside of the cell. Ribosomes | Back to Top Ribosomes are the sites of protein synthesis. They are not membrane-bound and thus occur in both prokaryotes and eukaryotes. Eukaryotic ribosomes are slightly larger than prokaryotic ones. Structurally the ribosome consists of a small and larger subunit. 10 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Biochemically the ribosome consists of ribosomal RNA (rRNA) and some 50 structural proteins. Often ribosomes cluster on the endoplasmic reticulum, in which case they resemble a series of factories adjoining a railroad line. Click here for Ribosomes (More than you ever wanted to know about ribosomes!) Structure of the ribosome. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 11 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Ribosomes and Polyribosomes - liver cell (TEM x173,400). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Endoplasmic reticulum | Back to Top Endoplasmic reticulum is a mesh of interconnected membranes that serve a function involving protein synthesis and transport. Rough endoplasmic reticulum (Rough ER) is so-named because of its rough appearance due to the numerous ribosomes that occur along the ER. Rough ER connects to the nuclear envelope through which the messenger RNA (mRNA) that is the blueprint for proteins travels to the ribosomes. Smooth ER; lacks the ribosomes characteristic of Rough ER and is thought to be involved in transport and a variety of other functions. The endoplasmic reticulum. Rough endoplasmic reticulum is on the left, smooth endoplasmic reticulum is on the right. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 12 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Rough Endoplasmic Reticulum with Ribosomes (TEM x61,560). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Golgi Apparatus and Dictyosomes | Back to Top Golgi Complexes are flattened stacks of membrane-bound sacs. They function as a packaging plant, modifying vesicles from the Rough ER. New membrane material is assembled in various cisternae of the golgi. 13 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Structure of the Golgi apparatus and its functioning in vesicle-mediated transport. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 14 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Golgi Apparatus in a plant parenchyma cell from Sauromatum guttatum (TEM x145,700). Note the numerous vesicles near the Golgi. This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Lysosomes | Back to Top Lysosomes are relatively large vesicles formed by the Golgi. They contain hydrolytic enzymes that could destroy the cell. Lysosome contents function in the extracellular breakdown of materials. 15 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Role of the Golgi in forming lysosomes. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Mitochondria | Back to Top Mitochondria contain their own DNA (termed mDNA) and are thought to represent bacteria-like organisms incorporated into eukaryotic cells over 700 million years ago (perhaps even as far back as 1.5 billion years ago). They function as the sites of energy release (following glycolysis in the cytoplasm) and ATP formation (by chemiosmosis). The mitochondrion has been termed the powerhouse of the cell. Mitochondria are bounded by two membranes. The inner membrane folds into a series of cristae, which are the surfaces on which ATP is generated. Structure of a mitochondrion. Image from Purves et al., Life: The Science of Biology, 4th Edition, 16 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Muscle Cell Mitochondrion (TEM x190,920). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Mitochondria and endosymbiosis During the 1980s, Lynn Margulis proposed the theory of endosymbiosis to explain the origin of mitochondria and chloroplasts from permanent resident prokaryotes. According to this idea, a larger prokaryote (or perhaps early eukaryote) engulfed or surrounded a smaller prokaryote some 1.5 billion to 700 million years ago. The basic events in endosymbiosis. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used 17 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... with permission. Instead of digesting the smaller organisms the large one and the smaller one entered into a type of symbiosis known as mutualism, wherein both organisms benefit and neither is harmed. The larger organism gained excess ATP provided by the "protomitochondrion" and excess sugar provided by the "protochloroplast", while providing a stable environment and the raw materials the endosymbionts required. This is so strong that now eukaryotic cells cannot survive without mitochondria (likewise photosynthetic eukaryotes cannot survive without chloroplasts), and the endosymbionts can not survive outside their hosts. Nearly all eukaryotes have mitochondria. Mitochondrial division is remarkably similar to the prokaryotic methods that will be studied later in this course. A summary of the theory is available by clicking here. Plastids | Back to Top Plastids are also membrane-bound organelles that only occur in plants and photosynthetic eukaryotes. Chloroplasts are the sites of photosynthesis in eukaryotes. They contain chlorophyll, the green pigment necessary for photosynthesis to occur, and associated accessory pigments (carotenes and xanthophylls) in photosystems embedded in membranous sacs, thylakoids (collectively a stack of thylakoids are a granum [plural = grana]) floating in a fluid termed the stroma. Chloroplasts contain many different types of accessory pigments, depending on the taxonomic group of the organism being observed. 18 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Structure of the chloroplast. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Chloroplasts and endosymbiosis Like mitochondria, chloroplasts have their own DNA, termed cpDNA. Chloroplasts of Green Algae (Protista) and Plants (descendants of some Green Algae) are thought to have originated by endosymbiosis of a prokaryotic alga similar to living Prochloron (Prochlorobacteria). Chloroplasts of Red Algae (Protista) are very similar biochemically to cyanobacteria (also known as blue-green bacteria [algae to chronologically enhanced folks like myself :)]). Endosymbiosis is also invoked for this similarity, perhaps indicating more than one endosymbiotic event occurred. Leukoplasts store starch, sometimes protein or oils. Chromoplasts store pigments associated with the bright colors of flowers and/or fruits. Cell Movement | Back to Top Cell movement; is both internal, referred to as cytoplasmic streaming and external, referred to as motility. Internal movements of organelles are governed by actin filaments. These filaments make an area in which organelles such as chloroplasts can move. Internal movement is known as cytoplasmic streaming. External movement of 19 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... cells is determined by special organelles for locomotion. The cytoskeleton. Image from Prentice Hall. Cilia and flagella are similar except for length, cilia being much shorter. They both have the characteristic 9 + 2 arrangement of microtubules. The 9+2 arrangement of microtubules in a flagellum or cilium. Image from Prentice Hall. 20 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Cilia from an epithelial cell in cross section (TEM x199,500). Note the 9 + 2 arrangement of cilia. This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Flagella work as whips pulling (as in Chlamydomonas or Halosphaera) or pushing (dinoflagellates, a group of single-celled Protista) the organism through the water. Cilia work like oars on a viking longship (Paramecium has 17,000 such oars covering its outer surface). 21 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Movement of cilia and flagella. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Pseudopodia are used by many cells, such as Amoeba, Chaos (Pelomyxa) and human leukocytes (white blood cells). These are not structures as such but rather are associated with actin near the moving edge. Formation and functioning of a pseudopod by an amoeboid cell. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Learning Objectives | Back to Top 22 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... Give the function and cellular location of the following basic eukaryotic organelles and structures: cell membrane, nucleus, endoplasmic reticulum, Golgi bodies, lysosomes, mitochondria, ribosomes, chloroplasts, vacuoles, and cell walls. A micrometer is one-millionth of a meter long. A nanometer is one-billionth of a meter long. How many micrometers tall are you? Describe the function of the nuclear envelope and nucleolus. Describe the details of the structure of the chloroplast, the site of photosynthesis. Mature, living plant cells often have a large, fluid-filled central vacuole that can store amino acids, sugars, ions, and toxic wastes. Animal cells generally lack large vacuoles. How do animal cells perform these functions? Microtubules, microfilaments, and intermediate filaments are all main components of the cytoskeleton. Flagella and cilia propel eukaryotic cells through their environment; the microtubule organization in these organelles is a 9+2 array. Terms | Back to Top actin carotenes chlorophyll cristae endoplasmic erythrocytes reticulum Green Algae hydrophilic mitochondria mutualism parenchyma phospholipid Red Algae ribosomal RNA vacuoles zygote cellulose cell walls cyanobacteria cytoplasm chemiosmosis chitin cytoskeleton dinoflagellates eukaryotic fluid-mosaic Golgi grana complexes hydrophobic leukocytes lysosomes microtubules neurons nucleus nucleolus ova photosystems plasmodesmata plastid pseudopodia ribosomes stroma symbiosis thylakoids Review Questions | Back to Top 1. There are ____ micrometers (µm) in one millimeter (mm). a) 1; b) 10; c) 100; d) 1000; e) 1/1000 2. Human cells have a size range between ___ and ___ micrometers (µm). a) 10-100; b) 1-10; c) 100-1000; d) 1/10-1/1000 3. Chloroplasts and bacteria are ___ in size. a) similar; b) at different ends of the size range; c) exactly the same; d) none of these. 4. The plasma membrane does all of these except ______. a) contains the hereditary material; b) acts as a boundary or border for the cytoplasm; c) regulates passage of material in and out of the cell; d) functions in the recognition of self 5. Which of these materials is not a major component of the plasma membrane? a) phospholipids; b) glycoproteins; c) proteins; d) DNA 6. Cells walls are found in members of these kingdoms, except for ___, which all lack cell walls. a) plants; b) animals; c) bacteria; d) fungi 7. The polysaccharide ___ is a major component of plan cell walls. a) chitin; b) peptidoglycan; c) cellulose; d) mannitol; e) cholesterol 8. Plant cells have ___ and ___, which are not present in animal cells. a) mitochondria, chloroplasts; b) cell membranes, cell walls; c) chloroplasts, nucleus; d) chloroplasts, cell wall 9. The ___ is the membrane enclosed structure in eukaryotic cells that contains the DNA of the cell. a) mitochondrion; b) chloroplast; c) nucleolus; d) nucleus 10. Ribosomes are constructed in the ___. a) endoplasmic reticulum; b) nucleoid; c) nucleolus; d) 23 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... nuclear pore 11. Rough endoplasmic reticulum is the area in a cell where ___ are synthesized. a) polysaccharides; b) proteins; c) lipids; d) DNA 12. The smooth endoplasmic reticulum is the area in a cell where ___ are synthesized. a) polysaccharides; b) proteins; c) lipids; d) DNA 13. The mitochondrion functions in ____. a) lipid storage; b) protein synthesis; c) photosynthesis; d) DNA replication; e) ATP synthesis 14. The thin extensions of the inner mitochondrial membrane are known as _____. a) cristae; b) matrix; c) thylakoids; d) stroma 15. The chloroplast functions in ____. a) lipid storage; b) protein synthesis; c) photosynthesis; d) DNA replication; e) ATP synthesis 16. Which of these cellular organelles have their own DNA? a) chloroplast; b) nucleus; c) mitochondrion; d) all of these 17. The theory of ___ was proposed to explain the possible origin of chloroplasts and mitochondria. a) evolution; b) endosymbiosis; c) endocytosis; d) cells 18. Long, whiplike microfibrils that facilitate movement by cells are known as ___. a) cilia; b) flagella; c) leather; d) pseudopodia Links | Back to Top Protist Image Data: Pictures and resources about Protista. Cell Biology Lab Manual: Lab protocols and links pertaining to cell biology. A nice place to look for new things to do in labs. MIT Hypertextbook Chapter on Cell Biology: Excellent site with illustrations and additional details to complement the above material. Virtual Plant Cell: Zoom in on a virtual plant cell. An excellent first step. WWW Cell Biology Course: An excellent site employing image maps and details about cell biology. Dictionary of Cell Biology: A searchable dictionary pertinent to this topic. Cells Alive! Very interesting site with new features each month. Ribosomes A text with links to illustrations. More than you ever wanted to know about ribosomes! Charlie and Bobby Jo's Excellent Adventure Look out, honey, I shrunk the lab! Humorous journey through a cell. (Dr. Sata, University of Texas). The Cell Nucleus This easily navigated series of well illustrated pages presents an impressive amount of information about the various functions carried out by the nucleus. References | Back to Top Text ©1992, 1994, 1997, 1998, 1999, 2000, 2001, by M.J. Farabee, all rights reserved. Use for educational purposes is heartily encouraged. Back to Table of Contents | Go to TRANSPORT IN AND OUT OF CELLS Email: mj.farabee@emcmail.maricopa.edu Last modified: 24 of 25 23/11/06 15:05 CELLS II: CELLULAR ORGANIZATION http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookCELL... The URL of this page is: 25 of 25 23/11/06 15:05 Reading(s) #2 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria Mitochondrion From Wikipedia, the free encyclopedia (Redirected from Mitochondria) In cell biology, a mitochondrion (plural mitochondria) (from Greek μιτος or mitos, thread + κουδριον or khondrion, granule) is a membrane-enclosed organelle, found in most eukaryotic cells.[1] Mitochondria are sometimes described as "cellular power plants," because they convert food molecules into energy in the form of ATP via the process of oxidative phosphorylation. A typical eukaryotic cell contains about 2,000 mitochondria, which occupy roughly one fifth of its total volume.[2] Mitochondria contain DNA that is independent of the DNA located in the cell nucleus. According to the endosymbiotic theory, mitochondria are descended from free-living prokaryotes. Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes Contents 1 Mitochondrion structure 1.1 Outer membrane 1.2 Inner membrane 1.3 Mitochondrial matrix 2 Mitochondrial functions 2.1 Energy conversion 2.1.1 Pyruvate: the citric acid cycle 2.1.2 NADH and FADH2: the electron transport chain 2.1.3 Heat production 2.1.4 Storage for calcium ions 3 Origin 4 Replication and gene inheritance 5 Use in population genetic studies 6 Fiction 7 Cited references 8 General references 9 External links 10 See also Mitochondrion structure 1 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria A mitochondrion contains inner and outer membranes composed of phospholipid bilayers and proteins. The two membranes, however, have different properties. Because of this double-membraned organization, there are 5 distinct compartments within mitochondria. There is the outer membrane, the intermembrane space (the space between the outer and inner membranes), the inner membrane, the cristae space (formed by infoldings of the inner membrane), and the matrix (space within the inner membrane). Mitochondria range from 1 to 10 micrometers (μm) in size. Outer membrane Simplified structure of a typical mitochondrion The outer mitochondrial membrane, which encloses the entire organelle, has a protein-to-phospholipid ratio similar to the eukaryotic plasma membrane (about 1:1 by weight). It contains numerous integral proteins called porins, which contain a relatively large internal channel (about 2-3 nm) that is permeable to all molecules of 5000 daltons or less.[3] Larger molecules can only traverse the outer membrane by active transport. It also contains enzymes involved in such diverse activities as the elongation of fatty acids, oxidation of epinephrine (adrenaline), and the degradation of tryptophan. Inner membrane The inner mitochondrial membrane contains proteins with four types of functions: [3] 1. 2. 3. 4. Those that carry out the oxidation reactions of the respiratory chain. ATP synthase, which makes ATP in the matrix. Specific transport proteins that regulate the passage of metabolites into and out of the matrix. Protein import machinery. It contains more than 100 different polypeptides, and has a very high protein-to-phospholipid ratio (more than 3:1 by weight, which is about 1 protein for 15 phospholipids). Additionally, the inner membrane is rich in an unusual phospholipid, cardiolipin, which is usually characteristic of bacterial plasma membranes. Unlike the outer membrane, the inner membrane does not contain porins, and is highly impermeable; almost all ions and molecules require special membrane transporters to enter or exit the matrix. In addition, there is a membrane potential across the inner membrane. The inner mitochondrial membrane is compartmentalized into numerous cristae, which expand the surface area of the inner mitochondrial membrane, enhancing its ability to generate ATP. In typical liver mitochondria, for example, the surface area, including cristae, is about five times that of the outer membrane. Mitochondria of cells which have greater demand for ATP, such as muscle cells, contain more cristae than typical liver mitochondria. Mitochondrial matrix 2 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria The matrix is the space enclosed by the inner membrane. The matrix contains a highly concentrated mixture of hundreds of enzymes, in addition to the special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome. Of the enzymes, the major functions include oxidation of pyruvate and fatty acids, and the citric acid cycle.[3] Image of cristae in rat liver mitochondrion Mitochondria possess their own genetic material, and the machinery to manufacture their own RNAs and proteins. (See: protein synthesis). This nonchromosomal DNA encodes a small number of mitochondrial peptides (13 in humans) that are integrated into the inner mitochondrial membrane, along with proteins encoded by genes that reside in the host cell's nucleus. Mitochondrial functions Although it is well known that the mitochondria convert organic materials into cellular energy in the form of ATP, mitochondria play an important role in many metabolic tasks, such as: Apoptosis-programmed cell death Glutamate-mediated excitotoxic neuronal injury Cellular proliferation Regulation of the cellular redox state Heme synthesis Steroid synthesis Some mitochondrial functions are performed only in specific types of cells. For example, mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism. A mutation in the genes regulating any of these functions can result in mitochondrial diseases. Energy conversion A dominant role for the mitochondria is the production of ATP as reflected by the large number of proteins in the inner membrane for this task. This is done oxidising the major products of glycolysis: pyruvate and NADH that are produced in the cytosol. This process of cellular respiration, also known as aerobic respiration, is dependent on the presence of oxygen. When oxygen is limited the glycolytic products will be metabolised by anaerobic respiration a process that is independent of the mitochondria. The production of ATP from glucose has an approximately 15 fold higher yield during aerobic respiration compared to anaerobic respiration. Pyruvate: the citric acid cycle Each pyruvate molecule produced by glycolysis is actively transported across the inner mitochondrial membrane, and into the matrix where it is oxidized and combined with coenzyme A to form CO2 , acetyl CoA and NADH. The acetyl CoA is the primary substrate to enter the citric acid cycle , also known as the tricarboxylic acid (TCA) cycle or Krebs cycle. The enzymes of the citric acid cycle are located in the mitochondrial matrix with the exception of succinate dehydrogenase, which is bound to the inner mitochondrial membrane. The citric acid cycle oxidises the acetyl CoA to carbon dioxide and in the process produces reduced cofactors (three molecules of NADH and one molecule of FADH2 ), that are a source of electrons for the electron transport 3 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria chain, and a molecule of GTP (that is readily converted to an ATP). NADH and FADH2 : the electron transport chain Pyruvate (from glycolysis) is made within the animal cell within the fluid. The redox energy from NADH and FADH2 is transferred to oxygen (O2) in several steps via the electron transport chain. These energy-rich molecules are produced within the matrix via the citric acid cycle but are also produced in the cytoplasm by glycolysis; reducing equivalents from the cytoplasm can be imported via the malate-aspartate shuttle system of antiporter proteins or feed into the electron transport chain using a glycerol phosphate shuttle. Protein Schematic of typical animal cell, showing complexes in the inner membrane (NADH dehydrogenase, subcellular components. Organelles: (1) nucleolus cytochrome c reductase and cytochrome c oxidase) perform (2) nucleus (3) ribosome (4) vesicle (5) rough the transfer and the incremental release of energy is used to endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria pump protons (H+) into the intermembrane space. This (10) vacuole (11) cytoplasm (12) lysosome (13) process is efficient but a small percentage of electrons may centrioles prematurely reduce oxygen, forming the toxic free radical superoxide. This can cause oxidative damage in the mitochondria and may contribute to the decline in mitochondrial function associated with the aging process.[4] As the proton concentration increases in the intermembrane space, a strong electrochemical gradient is established across the inner membrane. The protons can return to the matrix through the ATP synthase complex and their potential energy is used to synthesize ATP from ADP and inorganic phosphate (Pi ). This process is called chemiosmosis and was first described by Peter Mitchell who was awarded the 1978 Nobel Prize in Chemistry for his work. Later, part of the 1997 Nobel Prize in Chemistry was awarded to Paul D. Boyer and John E. Walker for their clarification of the working mechanism of ATP synthase. Heat production Under certain conditions, protons can re-enter the mitochondrial matrix without contributing to ATP synthesis. This process is known as proton leak or mitochondrial uncoupling and is due to the facilitated diffusion of protons into the matrix, mediated by a proton channel called thermogenin. This results in the unharnessed potential energy of the proton electrochemical gradient being released as heat. Thermogenin is found in brown adipose tissue (brown in colour due to high levels of mitochondria) where it is used to generate heat by non-shivering thermogenesis. Non-shivering thermogenesis is the primary means of heat generation in newborn or hibernating mammals. Storage for calcium ions The concentrations of free calcium in the cell can regulate an array of reactions and is important for signal transduction in the cell. Mitochondria store free calcium, a process that is one important event for the homestasis of calcium in the cell. Release of this calcium back into the cells interior can initiate calcium spikes or waves. These events coordinate processes such as neurotransmitter release in nerve cells and release of hormones in endocrine cells. 4 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria Origin As mitochondria contain ribosomes and DNA, and are only formed by the division of other mitochondria, it is generally accepted that they were originally derived from endosymbiotic prokaryotes. Studies of mitochondrial DNA, which is often circular and employs a variant genetic code, show their ancestor, the so-called proto-mitochondrion, was a member of the Proteobacteria.[5] In particular, the pre-mitochondrion was probably related to the rickettsias, although the exact position of the ancestor of mitochondria among the alpha-proteobacteria remains controversial. The endosymbiotic hypothesis suggests that mitochondria descended from specialized bacteria (probably purple non-sulfur bacteria) that somehow survived endocytosis by another species of prokaryote or some other cell type, and became incorporated into the cytoplasm. The ability of symbiont bacteria to conduct cellular respiration in host cells that had relied on glycolysis and fermentation would have provided a considerable evolutionary advantage. Similarly, host cells with symbiotic bacteria capable of photosynthesis would also have an advantage. In both cases, the number of environments in which the cells could survive would have been greatly expanded. This relationship developed at least 2 billion years ago and mitochondria still show some signs of their ancient origin. Mitochondrial ribosomes are the 70S (bacterial) type, in contrast to the 80S ribosomes found elsewhere in the cell. As in prokaryotes, there is a very high proportion of coding DNA, and an absence of repeats. Mitochondrial genes are transcribed as multigenic transcripts which are cleaved and polyadenylated to yield mature mRNAs. Unlike their nuclear cousins, mitochondrial genes are small, generally lacking introns, and many chromosomes are circular, conforming to the bacterial pattern. A few groups of unicellular eukaryotes lack mitochondria: the microsporidians, metamonads, and archamoebae. On rRNA trees these groups appeared as the most primitive eukaryotes, suggesting they appeared before the origin of mitochondria, but this is now known to be an artifact of long branch attraction — they are apparently derived groups and retain genes or organelles derived from mitochondria (e.g. mitosomes and hydrogenosomes).[1] There are no primitively amitochondriate eukaryotes, and so the origin of mitochondria may have played a critical part in the development of eukaryotic cells. Replication and gene inheritance Mitochondria replicate their DNA and divide mainly in response to the energy needs of the cell; in other words, their growth and division is not linked to the cell cycle. When the energy needs of a cell are high, mitochondria grow and divide. When the energy use is low, mitochondria are destroyed or become inactive. At cell division, mitochondria are distributed to the daughter cells more or less randomly during the division of the cytoplasm. Mitochondria divide by binary fission similar to bacterial cell division. Unlike bacteria, however, mitochondria can also fuse with other mitochondria. Sometimes new mitochondria are synthesized in centers that are rich in the proteins and polysomes needed for their synthesis. Mitochondrial genes are not inherited by the same mechanism as nuclear genes. At fertilization of an egg by a sperm, the egg nucleus and sperm nucleus each contribute equally to the genetic makeup of the zygote nucleus. In contrast, the mitochondria, and therefore the mitochondrial DNA, usually comes from the egg only. The sperm's mitochondria enters the egg, but are almost always destroyed and do not contribute their genes to the embryo.[6] Paternal sperm mitochondria are marked with ubiquitin to select them for later destruction inside the embryo.[7] The egg contains relatively few mitochondria, but it is these mitochondria that survive and divide to populate the cells of the adult organism. Mitochondria are, therefore, in most cases inherited down the female line. This maternal inheritance of mitochondrial DNA is seen in most organisms, including all animals. However, 5 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria mitochondria in some species can sometimes be inherited through the father. This is the norm amongst certain coniferous plants (although not in pines and yew trees).[8] It has been suggested to occur at a very low level in humans.[9] Uniparental inheritance means that there is little opportunity for genetic recombination between different lineages of mitochondria. For this reason, mitochondrial DNA is usually thought of as reproducing by binary fission. However, there are several claims of recombination in mitochondrial DNA, most controversially in humans. If recombination does not occur, the whole mitochondrial DNA sequence represents a single haplotype, which makes it useful for studying the evolutionary history of populations. Mitochondrial genomes have many fewer genes than do the related eubacteria from which they are thought to be descended. Although some have been lost altogether, many seem to have been transferred to the nucleus. This is thought to be relatively common over evolutionary time. A few organisms, such as Cryptosporidium, actually have mitochondria which lack any DNA, presumably because all their genes have either been lost or transferred. The uniparental inheritance of mitochondria is thought to result in intragenomic conflict, such as seen in the petite mutant mitochondria of some yeast species. It is possible that the evolution of separate male and female sexes is a mechanism to resolve this organelle conflict. Use in population genetic studies The near-absence of genetic recombination in mitochondrial DNA makes it a useful source of information for scientists involved in population genetics and evolutionary biology. Because all the mitochondrial DNA is inherited as a single unit, or haplotype, the relationships between mitochondrial DNA from different individuals can be represented as a gene tree. Patterns in these gene trees can be used to infer the evolutionary history of populations. The classic example of this is in human evolutionary genetics, where the molecular clock can be used to provide a recent date for mitochondrial Eve. This is often interpreted as strong support for a recent modern human expansion out of Africa. Another human example is the sequencing of mitochondrial DNA from Neanderthal bones. The relatively large evolutionary distance between the mitochondrial DNA sequences of Neanderthals and living humans has been interpreted as evidence for lack of interbreeding between Neanderthals and anatomically modern humans. However, mitochondrial DNA only reflects the history of females in a population, and so may not give a representative picture of the history of the population as a whole. For example, if dispersal is primarily undertaken by males, this will not be picked up by mitochondrial studies. This can be partially overcome by the use of patrilineal genetic sequences, if they are available (in mammals the non-recombining region of the Y-chromosome provides such a source). More broadly, only studies that also include nuclear DNA can provide a comprehensive evolutionary history of a population; unfortunately, genetic recombination means that these studies can be difficult to analyse. Fiction The midi-clorians of the Star Wars universe are fictional life-forms inside cells that provide the Force. George Lucas took inspiration from the endosymbiotic theory. Madeleine L'Engle's novel A Wind in the Door posits fictional "farandolae" which are to mitochondria what mitochondria are to cells. In Hideaki Sena's novel Parasite Eve (and the video game based on it), mitochondria are independent organisms, using animals and plants as a form of "transportation," causing a major biological disaster when they decide to set themselves free. 6 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria Cited references 1. ^ a b Henze, K., W. Martin (2003). "Evolutionary biology: Essence of mitochondria". Nature 426: 127-128. 2. ^ Voet, Donald, Judith G. Voet, Charlotte W. Pratt (2006). Fundamentals of Biochemistry, 2nd Edition. John Wiley and Sons, Inc., 547. ISBN 0-471-21495-7. 3. ^ a b c Alberts, Bruce, et. al. (1994). Molecular Biology of the Cell. New York: Garland Publishing Inc.. 4. ^ Huang, K., K. G. Manton (2004). "The role of oxidative damage in mitochondria during aging: A review". Frontiers in Bioscience 9: 1100-1117. 5. ^ Futuyma, Douglas J. (2005). "On Darwin's Shoulders". Natural History 114 (9): 64–68. 6. ^ Kimball, J.W. (2006) "Sexual Reproduction in Humans: Copulation and Fertilization," (http://home.comcast.net/~john.kimball1/BiologyPages/S/Sexual_Reproduction.html#Copulation_and_Fertilization Kimball's Biology Pages (based on Biology, 6th ed., 1996)] 7. ^ Sutovsky, P., et. al (Nov. 25, 1999). "Ubiquitin tag for sperm mitochondria". Nature 402: 371-372. DOI:10.1038/46466 (http://dx.doi.org/10.1038/46466) . Discussed in Science News (http://www.sciencenews.org/20000101/fob3.asp) . 8. ^ Mogensen, H. Lloyd (1996). "The Hows and Whys of Cytoplasmic Inheritance in Seed Plants". American Journal of Botany 83: 383-404. 9. ^ Johns, D. R. (2003). "Paternal transmission of mitochondrial DNA is (fortunately) rare". Annals of Neurology 54: 422-4. General references Cambell, Neil, et. al. (2006). Biology: concepts and connections. San Francisco: Benjamin Cummings. ISBN 0-8053-7160-5. National Center for Biotechnology Information (March 30, 2004). A Science primer (http://www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html) (English). Retrieved on July 9, 2006. Scheffler, I.E. (2001). "A century of mitochondrial research: achievements and perspectives". Mitochondrion 1 (1): 3–31. PDF (http://www.mitoresearch.org/century.pdf) External links Arthropod mitochondira (http://biology.plosjournals.org/perlserv/?request=get-document&doi=10%2E1371%2Fjournal%2Epbio%2E00401 Mitochondra Atlas (http://www.uni-mainz.de/FB/Medizin/Anatomie/workshop/EM/EMMitoE.html) Mitochondria Research Portal (http://www.mitochondrial.net) Mitochondria: Architecture dictates function (http://www.cytochemistry.net/Cell-biology/mitoch1.htm) Mitochondira links (http://bama.ua.edu/~hsmithso/class/bsc_495/mito-plastids/mito_web.html) Mitochondrion Reconstructed by Electron Tomography (http://www.sci.sdsu.edu/TFrey/MitoMovie.htm) Mitochondrion with Cell Biology (http://www.zytologie-online.net/mitochondrium.php) Review of evidence addressing whether mitochondria form cellular networks or exist as discrete organelles (http://www.the-elso-gazette.org/magazines/issue11/mreviews/mreviews1.asp) Video Clip of Rat-liver Mitochondrion from Cryo-electron Tomography (http://www.wadsworth.org/databank/electron/cryomito_dis2.html) Information on Mitochondrial Diseases (http://www.circuitblue.com/mito) Mitochondria and Aging (http://www.circuitblue.com/biogerontology/mito.shtml) 3D structures of proteins from inner mitochondrial membrane (http://opm.phar.umich.edu/localization.php?localization=Mitochondrial%20inner%20membrane) 3D structures of proteins associated with outer mitochondrial membrane (http://opm.phar.umich.edu/localization.php?localization=Mitochondrial%20outer%20membrane) See also 7 of 8 23/11/06 15:06 Mitochondrion - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Mitochondria Anti-mitochondrial antibodies Chemiosmotic hypothesis Chloroplast Electrochemical potential Endosymbiotic theory Glycolysis Mitochondrial disease Mitochondrial DNA Human mitochondrial genetics Mitochondrial permeability transition pore Submitochondrial particle Wikimedia Commons has media related to: Mitochondrion Organelles of the cell Acrosome | Cell wall | Cell membrane | Chloroplast | Cilium/Flagellum | Centrosome | Cytoplasm | Endoplasmic reticulum | Endosome | Golgi apparatus | Lysosome | Melanosome | Mitochondrion | Myofibril | Nucleus | Nucleolus (sub-organelle, found within the nucleus) | Parenthesome | Peroxisome | Plastid | Ribosome | Vacuole | Vesicle This article contains material from the Science Primer (http://www.ncbi.nlm.nih.gov/About/Primer) published by the NCBI, which, as a US government publication, is in the public domain Retrieved from "http://en.wikipedia.org/wiki/Mitochondrion" Categories: Cellular respiration | Organelles This page was last modified 16:34, 22 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 8 of 8 23/11/06 15:06 Reading(s) #3 Organelle - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Organelles Organelle From Wikipedia, the free encyclopedia (Redirected from Organelles) In cell biology, an organelle is a discrete structure of a cell having specialized functions. There are many types of organelles, particularly in the eukaryotic cells of higher organisms. An organelle is to the cell what an organ is to the body (hence the name organelle, the suffix -elle being a diminutive). Organelles were historically identified through the use of microscopy, and were also identified through the use of cell fractionation. A few large organelles probably originated from endosymbiont bacteria: mitochondria (in almost all eukaryotes) plastids (in plants and algae) chloroplasts, mature forms of etioplasts chromoplasts leucoplasts amyloplasts statoliths elaioplasts proteinoplasts rhodoplasts Schematic of typical animal cell, showing subcellular components. Organelles: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles Other organelles have had endosymbiotic origins suggested for them (notably flagella; see Evolution of flagella), but these theories are not widely accepted. Contents 1 2 3 4 Eukaryotic organelles Prokaryotic organelles See also References Eukaryotic organelles Eukaryotes are the most structurally complex known cell type, and by definition are in part organized by smaller interior compartments, that are themselves enclosed by lipid membranes that resemble the outermost cell membrane. The larger organelles, such as the nucleus and vacuoles, are easily visible with moderate magnification (although sometimes a clear view requires the application of chemicals that selectively stain parts of the cells); they were among the first biological discoveries made after the invention of the 1 of 4 23/11/06 15:07 Organelle - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Organelles microscope. Not all eukaryotic cells have all of the organelles listed below, and occasionally, exceptional species of cells are missing organelles which might otherwise be considered universal to eukaryotic cells (such as mitochondria). There are also occasional exceptions to the number of membranes surrounding organelles, listed in the tables below (e.g. some which are listed as double-membraned are sometimes found with single or triple membranes). Major eukaryotic organelles Organelle Main function Structure Organisms chloroplast (plastid) photosynthesis double-membrane compartment plants, protists endoplasmic reticulum modification and folding of new proteins and lipids single-membrane compartment all eukaryotes Golgi apparatus sorting and modification of proteins single-membrane compartment most eukaryotes mitochondrion energy production double-membrane compartment most eukaryotes vacuole storage & homeostasis single-membrane compartment eukaryotes nucleus DNA maintenance & transcription to RNA double-membrane compartment all eukaryotes Notes has some genes has some genes has bulk of genome Organelles which have double-membranes and their own DNA are believed by many biologists of having originally come from incompletely consumed or invading prokaryotic cells, which were adopted as a part of the invaded cell through endosymbiosis. Originally, the word organelle referred to large lipid bags within cells; later, as other cell parts were discovered, the meaning was extended to also include smaller parts of cells. Other eukaryotic organelles and cell components Organelle Main function Organisms acrosome helps spermatoza fuse with ovum single-membrane compartment many animals centriole anchor for cytoskeleton Microtubule protein animals cilium movement in or of external medium Microtubule protein animals, protists, few plants glyoxysome conversion of fat into sugars single-membrane compartment plants double-membrane compartment a few unicellular eukaryotes energy & hydrogen hydrogenosome production 2 of 4 Structure lysosome single-membrane breakdown of large molecules compartment melanosome pigment storage single-membrane compartment most eukaryotes animals 23/11/06 15:07 Organelle - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Organelles mitosome not characterized double-membrane compartment a few unicellular eukaryotes myofibril muscular contraction bundled filaments animals nucleolus ribosome production protein-DNA-RNA most eukaryotes parenthesome not characterized not characterized fungi peroxisome oxidation of protein single-membrane compartment all eukaryotes ribosome translation of RNA into proteins RNA-protein eukaryotes & prokaryotes vesicle miscellaneous single-membrane compartment all eukaryotes Other related structures: cytosol endomembrane system nucleosome microtubule cell membrane Prokaryotic organelles Prokaryotes are not as structurally complex as eukaryotes, and do not have any compartments enclosed by lipid membranes. In the past they were often viewed as having little internal organization, but slowly details are emerging about prokaryotic internal structures. One contributing discovery was that at least some prokaryotes have microcompartments, which are compartments enclosed by proteins. Prokaryotic organelles and cell components Organelle Main function Structure Organisms carboxysome carbon fixation protein-shell compartment some bacteria flagellum protein filament some prokaryotes and eukaryotes inorganic crystal, protein magnetotactic bacteria movement in external medium magnetosome magnetic orientation nucleoid DNA maintenance & transcription to RNA DNA-protein prokaryotes plasmid DNA exchange circular DNA some bacteria ribosome translation of RNA into proteins RNA-protein eukaryotes & prokaryotes See also Cell Endosymbiotic theory 3 of 4 23/11/06 15:07 Organelle - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Organelles References Alberts, Bruce et al. (2002). The Molecular Biology of the Cell, 4th ed., Garland Science, 2002, ISBN 0-8153-3218-1. Kerfeld, Cheryl A et al., Protein Structures Forming the Shell of Primitive Bacterial Organelles, Science 309:936-938 (5 August 2005). Organelles of the cell Acrosome | Cell wall | Cell membrane | Chloroplast | Cilium/Flagellum | Centrosome | Cytoplasm | Endoplasmic reticulum | Endosome | Golgi apparatus | Lysosome | Melanosome | Mitochondrion | Myofibril | Nucleus | Nucleolus (sub-organelle, found within the nucleus) | Parenthesome | Peroxisome | Plastid | Ribosome | Vacuole | Vesicle Retrieved from "http://en.wikipedia.org/wiki/Organelle" Category: Cell biology This page was last modified 19:31, 19 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 4 of 4 23/11/06 15:07 Reading(s) #4 Cell Membranes Problem Set http://www.biology.arizona.edu/cell_bio/problem_sets/membranes/i... The Biology Project > Cell Biology > Cell Membranes > List of Problems Cell Membranes Tutorial This exercise introduces the dynamic complexes of proteins, carbohydrates, and lipids that comprise cell membranes. You should learn that membranes are fluid, with components that move, change, and perform vital physiological roles as they allow cells to communicate with each other and their environment. We also show that membranes also are important for regulating ion and molecular traffic flow between cells,and that defects in membrane components lead to many significant diseases. Instructions: The following problems have multiple choice answers. Correct answers are reinforced with a brief explanation. Incorrect answers are linked to tutorials to help solve the problem. Overview 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Membrane components Lipids and aqueous barriers Hydrophobic forces Osmosis Membrane transport Membrane proteins Diffusion Cotransport Water flow solution Membrane stability Phospholipids Penetrating lipid bilayer Cell junctions Energy requirements for transport Oral rehydration Membrane flow The Biology Project > Cell Biology > Cell Membranes > List of Problems Credits The Biology Project Department of Biochemistry and Molecular Biophysics University of Arizona May 2002 Revised: August 2004 Contact the Development Team http://www.biology.arizona.edu All contents copyright © 2002-04. All rights reserved. 1 of 1 31/03/07 06:01 Reading(s) #5 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus Cell nucleus From Wikipedia, the free encyclopedia In cell biology, the nucleus (pl. nuclei; from Latin nucleus or nuculeus, kernel) is a membrane-enclosed organelle found in most eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins such as histones to form chromosomes. The genes within these chromosomes make up the cell's nuclear genome. The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression. Gene expression involves two major processes, the first of which is transcription, in which DNA The eukaryotic cell nucleus. Visible in this diagram are the is used as a template to produce RNA. When this ribosome-studded double membranes of the nuclear envelope, the RNA encodes proteins, it is referred to as DNA (complexed as chromatin), and the nucleolus. Within the messenger RNA (mRNA). The second process is cell nucleus is a viscous liquid called nucleoplasm, similar to the called translation, and involves mRNA being used cytoplasm found outside the nucleus. as a template to produce proteins. Only transcription occurs inside the nucleus, meaning that all mRNA must be exported to the cytoplasm before it can be translated. The main structural elements of the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle, and the nuclear lamina, a meshwork on the nuclear face of the envelope that adds mechanical support. Because the membranes are impermeable to most molecules, nuclear pores are required to allow movement across the envelope. These pores cross the entire envelope, providing a channel that allows free movement of small solutes. The movement of larger molecules is controlled, and requires active transport, facilitated by carrier proteins. Nuclear transport is of paramount importance to cell function, as movement through the pores is required for both gene expression and chromosomal maintenance. Although the interior of the nucleus does not contain any membrane-delineated bodies, its contents are not uniform, and a number of subnuclear bodies exist, made up of unique proteins, RNA molecules, and DNA conglomerates. The best known of these is the nucleolus, which is mainly involved in assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA. The nucleus was the first organelle to be discovered, and was first described by Franz Bauer in 1802.[1] It was later popularized by Scottish botanist Robert Brown in 1831. Brown was studying orchids microscopically when he observed an opaque area, which he called the areola or nucleus, in the cells of the flower's outer layer.[2] 1 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus Contents 1 Structure 1.1 Nuclear envelope and pores 1.2 Cytoskeleton 1.3 Chromosomes 1.4 Nucleolus 1.5 Other subnuclear bodies 1.5.1 Cajal bodies 1.5.2 Gemini of coiled bodies 1.5.3 Nemaline rods 1.5.4 PML bodies 1.5.5 Speckles 2 Function 2.1 Cell compartmentation 2.2 Gene expression 2.2.1 Processing of pre-mRNA 3 Dynamics and regulation 3.1 Nuclear transport 3.2 Assembly and disassembly 3.2.1 During the cell cycle 3.2.2 During apoptosis 3.2.3 During viral infection 4 Anucleated and polynucleated cells 5 Evolution 6 References 7 Further reading 8 External links Structure The nucleus is the largest cellular organelle.[3] It varies in diameter from 11 to 22 μm and occupies about 10% of the total cell volume.[4] The viscous liquid within it is called nucleoplasm, and is similar to the cytoplasm found outside the nucleus. Nuclear envelope and pores 2 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus The nuclear envelope consists of two cellular membranes, an inner and an outer membrane, arranged parallel to one another and separated by 10 to 50 nm. One of the features that make the nuclear membranes unique are the large pores they contain. The nuclear envelope encloses the nucleus and separates the cell's genetic material from the surrounding cytoplasm, serving as a barrier to prevent macromolecules from diffusing freely between the nucleoplasm and the cytoplasm.[5] The outer nuclear membrane is continuous with the membrane of the rough endoplasmic reticulum (RER), and is similarly studded with ribosomes. The space between the membranes is called the perinuclear space and is continuous with the RER lumen. A cross section of a nuclear pore on the surface of the nuclear envelope (1). Other diagram lables show (2) the outer ring, (3) spokes, (4) basket, and (5) filaments. Nuclear pores, which provide aqueous channels through the envelope, are composed of a number of different proteins, collectively referred to as nucleoporins. The pores are about 125 million daltons in molecular weight and consist of around 50 (in yeast) to 100 proteins (in vertebrates).[3] The pores are 100 nm in diameter; however, after the annulus and other regulatory gating system molecules are present, the space left for molecules to enter is reduced to 9 nm. This size allows the free passage of small water-soluble molecules whilst excluding larger structures, such as DNA or proteins. Large molecules can still enter the nucleus, but need to be transported. The nucleus of a typical mammalian cell will have about 3000 to 4000 pores throughout its envelope.[6] Most proteins, ribosomal subunits, and some RNAs are transported through the pore complexes in a process mediated by a family of transcription factors known as karyopherins. Those karyopherins that mediate movement into the nucleus are also called importins, while those that mediate movement out of the nucleus are called exportins. Most karyopherins interact directly with their cargo, although some use adaptor proteins.[7] Steroid hormones such as cortisol and aldosterone, as well as other small lipid-soluble molecules involved in intercellular signaling can diffuse through the cell membrane and into the cytoplasm, where they bind nuclear receptor proteins that are trafficked into the nucleus. There they serve as transcription factors when bound to their ligand; in the absence of ligand many such receptors function as histone deacetylases that repress gene expression.[3] Cytoskeleton Two networks of intermediate filaments provide the nucleus with mechanical support: the nuclear lamina forms an organised meshwork on the nuclear face of the envelope; less organised support is provided on the cystolic face of the envelope. The mechanical functions provided include structural support for the nuclear envelope, as well as providing anchorage sites for chromosomes and nuclear pores.[4] The nuclear lamina is mostly composed of lamin proteins. The lamin proteins are transported into the nucleus interior, where they are assembled, before being incorporated into the nuclear lamina.[8][9] In addition to their role in the lamina, lamin proteins are also found inside the nucleoplasm where they form 3 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus another regular structure,[10] called the nucleoplasmic veil. Like other intermediate filaments, the nuclear lamina monomer, the lamin, contains an alpha-helical region. This domain is used by two monomers to coil around each other, facing the same direction, and form a dimer structure called a coiled coil. Two of these dimer structures then join side by side, in an antiparallel arrangement, to form a tetramer. This tetramer, composed of four lamin proteins, is called a protofilament. Eight of these protofilaments form a lateral arrangement that is twisted to form a ropelike filament. These filaments can be assembled or disassembled in a dynamic manner, meaning that changes in length depend on the competing rates of filament addition and removal.[4] Chromosomes The cell nucleus contains the majority of the cell's genetic material, in the form of DNA molecules. During most of the cell cycle these are organized in a DNA-protein complex known as chromatin, and during cell division the chromatin can be seen to form well defined chromosomes. There are two types of chromatin: euchromatin which is the less compact DNA form, and which contains genes that are frequently expressed by the cell;[11] heterochromatin which is the more compact form, and contains DNA that is not transcribed. It is further categorized into facultative heterochromatin, consisting of those non-expressed genes, and constitutive heterochromatin, which consists of DNA's structural components, telomeres and centromeres. During interphase the chromatin organise themselves into discrete individual patches,[12] called chromosome territories.[13] Active genes, which are generally found in the euchromatic region of the chromosome, tend to be located towards the chromosome's territory boundary.[14] Nucleolus The nucleolus is a discrete densely-stained structure found in the nucleus. It is not surrounded by a membrane, and is sometimes called a suborganelle. It forms around tandem repeats of rDNA, DNA coding for ribosomal RNA (rRNA). These regions are called nucleolar organizer regions (NOR). The main roles of the nucleolus are to synthesize rRNA and assemble ribosomes. The structural cohesion of the nucleolus depends on its activity, as ribosomal assembly in the nucleolus results in the transient association of nucleolar components, facilitating further ribosomal assembly, and hence further association. This model is supported by observations that inactivation of rDNA results in intermingling of nucleolar structures.[15] An electron micrograph of a cell nucleus, showing the darkly stained nucleolus. The first step in ribosomal assembly is transcription of the rDNA, by a protein called RNA polymerase I, forming a large pre-rRNA precursor. This is cleaved into the subunits 5.8S, 18S, and 28S rRNA.[16] The transcription, post-transcriptional processing, and assembly of rRNA occurs in the nucleolus, aided by small nucleolar RNA (snoRNA) molecules, some of which are derived from spliced introns from messenger RNAs encoding genes related to ribosomal function. The assembled ribosomal subunits are the largest structures passed through the nuclear pores.[3] 4 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus When observed under the electron microscope, the nucleolus can be seen to consist of three distinguishable regions: the inner most fibrillar centers (FCs), surrounded by the dense fibrillar component (DFC), which in turn is bordered by the granular component (GC). Transcription of the rDNA occurs either in the FC or at the FC-DFC boundary, and therefore when rDNA transcription in the cell is increased more FCs are detected. Most of the cleavage and modification of rRNAs occurs in the DFC, while the latter steps involving protein assembly onto the ribosomal subunits occurs in the GC.[16] Other subnuclear bodies Besides the nucleolus, the nucleus contains a number of other non-membrane delineated bodies. These include Cajal bodies, Gemini of coiled bodies, paraspeckles, polymorphic interphase karyosomal association (PIKA), PML bodies, and speckles. Although little is known about a number of these domains, they are significant in that they show that the nucleoplasm is not uniform mixture, but rather contains organised functional subdomains.[19] Cajal bodies Subnuclear structure sizes Structure name Structure diameter Cajal bodies 0.2-2.0 μm [17] PIKA 5 μm [18] PML bodies 0.2-1.0 μm [19] Speckles 20–25 nm[18] A nucleus will contain between 1 and 10 compact structures called Cajal bodies (CB). The diameter of which measure between 0.2 μm and 2.0 μm depending on the cell type and species,[17] and when seen under an electron microscope, appear as balls of tangled thread.[18] They are involved in a number of different roles relating to RNA processing, specifically small nucleolar RNA (snoRNA) and small nuclear RNA (snRNA) maturation, and histone mRNA modification.[17] Gemini of coiled bodies Similar to Cajal bodies are Gemini of coiled bodies, also called Gems. The name is derived from the Gemini constellation, the twins, in reference to Gems' close association with CBs. They are similar in size and shape to CBs, but differ in composition. Unlike CBs, Gems don't contain snRNPs, but do contain a protein called survivor of motor neurons (SMN) whose function relates to snRNP biogenesis. Gems are believed to assist CBs in snRNP biogenesis.[20] Nemaline rods The presence of small intranuclear rods have been reported in some cases of nemaline myopathy. This condition typically results from mutations in actin, and the rods themsleves consist of mutant actin as well as other cytoskeletal proteins.[21] PML bodies Promyelocytic leukaemia bodies (PML bodies) are spherical bodies found scattered throughout the nucleoplasm, measuring around 0.2-1.0 μm. They are known by a number of other names, including nuclear domain 10 (ND10), Kremer bodies, and PML oncogenic domains. They are often seen in the nucleus in association with Cajal bodies and cleavage bodies. It has been suggested that they play a role in regulating transcription.[19] 5 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus Speckles Sometimes referred to as interchromatin granule clusters, speckles are rich in splicing snRNPs and other splicing proteins necessary for pre-mRNA processing. Because of a cell's changing requirements, the composition and location of these bodies changes according to mRNA transcription and regulation via phosphorylation of specific proteins.[22] Function The main functions of the nucleus are providing a compartment separated from the rest of the cell and controlling transcription. Cell compartmentation The nuclear envelope allows the nucleus to control its contents, and separate them from the rest of the cytoplasm where necessary. This is important for controlling processes on either side of the nuclear membrane. For example: In some cases where a cytoplasmic process needs to be restricted, a key participant is removed to the nucleus. For example this occurs in the case of glycolysis, a cellular pathway for breaking down glucose to produce energy. Hexokinase is an enzyme responsible for the first the step of glycolysis, forming glucose-6-phosphate from glucose. At high concentrations of fructose-6-phosphate, a molecule made later from glucose-6-phosphate, a regulator protein removes hexokinase to the nucleus.[23] In order to control which genes are being transcribed, the cell separates the proteins controlling gene expression from those genes. For example in the case of NF-κB genes, which are involved in most inflammatory responses, the genes are transcribed in response to a signal pathway. In one of the pathways involving these genes, TNF-α binds to a cell membrane receptor resulting in the recruitment of signalling proteins, and eventually freeing NF-κB. The nuclear localisation signal allows NF-κB to be transported through the nuclear pore and into the nucleus where it stimulates the transcription of the target genes.[4] The compartmentation allows the cell to prevent translation of unspliced mRNA.[24] Eukaryotic mRNA contains introns that must be removed before being translated to produce functional proteins. The splicing is done inside the nucleus before the mRNA can be accessed by ribosomes for translation. Without the nucleus ribosomes would translate newly transcribed (unprocessed) mRNA resulting in misformed proteins. 6 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus Gene expression Gene expression first involves transcription, in which DNA is used as a template to produce RNA. In the case of genes encoding proteins, that RNA produced from this process is messenger RNA (mRNA), which then needs to be translated by ribosomes to form a protein. As ribosomes are located outside the nucleus, mRNA produced needs to be exported. A micrograph of ongoing gene transcription of ribosomal RNA illustrating the growing primary transcripts. "Begin" indicates the 5' end of the DNA, where new RNA synthesis begins; "end" indicates the 3' end, where the primary transcripts are almost complete. Since the nucleus is the site of transcription, it also contains a variety of proteins which either directly mediate transcription or are involved in regulating the process. These proteins include helicases that unwind the double-stranded DNA molecule to facilitate access to it, RNA polymerases that synthesize the growing RNA molecule, topoisomerases that restore the supercoiled state of DNA after it has been unwound, and a large variety of transcription factors that regulate expression. Processing of pre-mRNA Newly synthesized mRNA molecules are known as primary transcripts or pre-mRNA. They must undergo post-transcriptional modification in the nucleus before being exported to the cytoplasm; mRNA that appears in the nucleus without these modifications is degraded rather than used for protein translation. The three main modifications are 5' capping, 3' polyadenylation, and RNA splicing. While in the nucleus, pre-mRNA is associated with a variety of proteins in complexes known as heterogeneous ribonucleoprotein particles (hnRNPs). Addition of the 5' cap occurs co-transcriptionally and is the first step in post-translational modification. The 3' poly-adenine tail is only added after transcription is complete. RNA splicing, carried out by a complex called the spliceosome, is the process by which introns, or regions of DNA that do not code for protein, are removed from the pre-mRNA and the remaining exons connected to re-form a single continuous molecule. This process normally occurs after 5' capping and 3' polyadenylation but can begin before synthesis is complete in transcripts with many exons.[3] Many pre-mRNAs, including those encoding antibodies, can be spliced in multiple ways to produce different mature mRNAs that encode different protein sequences. This process is known as alternative splicing, and allows production of a large variety of proteins from a limited amount of DNA. Dynamics and regulation The nucleus is a dynamic structure that changes according the cell's requirements. In order to control the nuclear functions, the processes of entry and exit from the nucleus are regulated. Nuclear transport 7 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus The entry and exit of large molecules from the nucleus is tightly controlled by the nuclear pore complexes. Although small molecules can enter the nucleus without regulation,[25] macromolecules such as RNA and proteins require association karyopherins called importins to enter the nucleus and exportins to exit. "Cargo" proteins that must be translocated from the cytoplasm to the nucleus contain short amino acid sequences known as nuclear localization signals which are bound by importins, while those transported from the nucleus to the cytoplasm carry nuclear export signals bound by exportins. The ability of Macromolecules, such as RNA and proteins, are actively importins and exportins to transport their cargo transported across the nuclear membrane in a process called the is regulated by GTPases, enzymes that Ran-GTP nuclear transport cycle. hydrolyze the molecule guanosine triphosphate to release energy. The key GTPase in nuclear transport is Ran, which can bind either GTP or GDP (guanosine diphosphate) depending on whether it is located in the nucleus or the cytoplasm. Whereas importins depend on RanGTP to dissociate from their cargo, exportins require RanGTP in order to bind to their cargo.[7] Nuclear import depends on the importin binding its cargo in the cytoplasm, carrying it through the nuclear pore into the nucleus. Inside the nucleus RanGTP acts to separate the cargo from the importin, allowing the importin to exit the nucleus and be reused. Nuclear export is similar, as the exportin binds the cargo inside the nucleus, leaves through the nuclear pore, and by interacting with RanGDP separates. Specialized export proteins exist for translocation of mature mRNA and tRNA to the cytoplasm after post-transcriptional modification is complete. This quality-control mechanism is important due to the these molecules' central role in protein translation; mis-expression of a protein due to incomplete excision of exons or mis-incorporation of amino acids could have negative consequences for the cell; thus incompletely modified RNA that reaches the cytoplasm is degraded rather than used in translation.[3] Assembly and disassembly During its lifetime a nucleus may be broken down, a process which depending on the circumstances may eventually be followed by its being reconstructed. During these events, the main components whose break down needs to be controlled are the structural ones, namely the nuclear envelope and the nuclear lamina. During the cell cycle 8 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus During the cell cycle the cell divides to form two cells. In order for this process to be possible, each of the new daughter cells must have a full set of genes, a process requiring replication of the chromosomes as well as segregation of the separate sets. This requires that the replicated chromosomes, the sister chromatids, be attached to microtubules, which in turn are attached to different centrosomes. The sister chromatids can then be pulled to separate locations in the cell. However, in many cells the centrosome is located in the cytoplasm, outside the nucleus, the microtubles would be unable to attach to the chromatids in the presence of the An image of a newt lung cell stained with fluorescent dyes during anaphase. The mitotic spindles can be seen, stained green, attached to the two sets of chromosomes, stained light blue. Each complete set of chromosomes is being pulled by the spindle towards its own centrosomes, also stained green. nuclear envelope.[26] Therefore the early stages in the cell cycle, beginning in prophase and until around prometaphase, the nuclear membrane is dismantled.[10] Likewise, during the same period, the nuclear lamina is also dissembled, a process regulated by phosphoyrlation of the lamins. Towards the end of the cell cycle, the nuclear membrane is reformed, and around the same time, the nuclear lamina reassembled by dephosphorylating the lamins.[10] During apoptosis Apoptosis is a controlled process resulting in death of the cell. Various of the changes directly affect the nucleus and its contents, especially condensation of the chromatin, disintegration of the nuclear envelope and lamina. The progressive organisation of the nuclear lamina throughout apoptosis is used to initiate and regulate the various phases of apoptosis.[10] The breakdown of the lamina is controlled by a group of proteins called caspases that cleave the individual lamins. During viral infection The nuclear envelope acts as a barrier that prevents both DNA and RNA viruses from entering the nucleus. Some viruses require access to proteins inside the nucleus in order to replicate and/or assemble. DNA viruses, such as herpesvirus replicate and assemble in the cell nucleus, and exit by budding through the inner nuclear membrane. This process is accompanied by disassembly of the lamina on the nuclear face of the inner membrane.[10] Anucleated and polynucleated cells 9 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus Although most cells have a single nucleus, some cell types can have none or many nuclei. This can be a normal process, as in the maturation of mammalian red blood cells, or an abnormal product of faulty cell division. Anucleated cells contain no nucleus and are therefore incapable of dividing to produce daughter cells. The best-known anucleated cell is the mammalian red blood cell, or erythrocyte, which also lacks other organelles such as mitochondria and serves primarily as a transport vessel to ferry oxygen from the lungs to the body's tissues. Erythrocytes mature via erythropoiesis in the bone marrow, where they lose their nuclei, organelles, and ribosomes. The nucleus is expelled during the process of differentiation from an erythroblast to a reticulocyte, the immediate precursor of the mature erythrocyte.[27] The presence of mutagens may induce the release of some immature "micronucleated" erythrocytes into the bloodstream.[28][29] Anucleated cells can also arise from flawed cell division in which one daughter lacks a nucleus and the other is binucleate. Human red blood cells, like those of other mammals, lack nuclei. This occurs as a normal part of the cells' development. Polynucleated cells contain multiple nuclei. Most Acantharean species of protozoa[30] and some fungi in mycorrhizae[31] have naturally polynucleated cells. Cells arising from the fusion of monocytes and macrophages, known as giant multinucleated cells, sometimes accompany inflammation[32] and are also implicated in tumor formation.[33] Evolution There are four contending theories of the origin of the nucleus in eukaryotic cells.[34] One theory proposed by Purificacion Lopez-Garcia and David Moreira is the syntrophic model. This model holds that a symbiotic relationship between the archaea and bacteria created the nucleus containing eukaryotic cell. It is believed that archaea, similar to modern methanogenic archaea, entered bacteria, similar to modern myxobacteria, and developed a symbiosis which eventually fused into a chimeric new organism the eukarya. An archaeal origin of the nucleus is supported by observations that archaea and eukarya have similar genes for certain proteins, including histones. Observations that myxobacteria are motile, can form multicelluar complexes, and possess kinases and G proteins similar to eukarya, supports a bacterial origin for the eukaryotic cell.[35] Another model by John Fuerst proposes that eukaryotic like cells existed at the same time as archaea and bacteria were splitting off on their own lineages. This model is based on the existence of modern planctomycetes bacteria that possess a nuclear structure with primitive pores and other compartmentalized membrane structures.[36] A similar proposal states that a eukarya like cell, the chronocyte, evolved first and phagocytosed archaea and bacteria to generate the nucleus and the eukaryotic cell.[37] The third and most controversial model, known as viral eukaryogenesis, posits that the membrane-bound nucleus, along with other eukaryotic features, originated from the infection of a prokaryote by a virus. The suggestion is based on similarities between eukaryotes and viruses such as linear DNA strands, mRNA capping, and tight binding to proteins (analogizing histones to viral envelopes). One version of the proposal suggests that the nucleus evolved in concert with phagocytosis to form an early cellular "predator".[38] Another variant proposes that eukaryotes originated from early archaea infected by poxviruses, on the basis of observed similarity between the DNA polymerases in modern poxviruses and eukaryotes.[39][40] It has been suggested that the as-yet-unresolved question of the evolution of sex could be related to the viral 10 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus eukaryogenesis hypothesis.[41] The fourth model proposed by Albert de Roos is based on the self assembly of membranes by lipid-protein interactions. The model is based on a Darwinist approach of the evolution of compartmentalization of function by interaction of laminar proteins, intrinsic proteins, and cytoskeletal proteins with lipid vesicles to form the nucleus, and exomembranes to form the endoplasmic reticulum and plasma membrane.[42] References 1 . ^ Harris, H (1999). The Birth of the Cell. New Haven: Yale 13. University Press. 2 . ^ Brown, Robert (1866). "On the Organs and Mode of Fecundation of Orchidex and Asclepiadea". Miscellaneous 14. Botanical Works I: 511-514. 3 . ^ a b c d e f Lodish, H, Berk A, Matsudaira P, Kaiser CA, Krieger M, Scott MP, Zipursky SL, Darnell J. (2004). Molecular Cell Biology, 5th, New York: WH Freeman. 4 . ^ a b c d (2002) Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter Molecular 15. Biology of the Cell, 4th, Garland Science. 5 . ^ Paine PL, Moore LC, Horowitz SB. Nuclear envelope permeability. Nature. 1975 Mar 13;254(5496):109-14. PMID 1117994 6 . ^ (1996) “Ch3”, Rodney Rhoades, Richard Pflanzer Human 16. Physiology, 3rd, Saunders College Publishing. 7 . ^ a b Pemberton, Lucy F., Bryce M. Paschal (2005). "Mechanisms of Receptor-Mediated Nuclear Import and 17. Nuclear Export". Traffic 6: 187-198. DOI:10.1111/j.1600-0854.2005.00270.x (http://dx.doi.org/10.1111/j.1600-0854.2005.00270.x) . 8 . ^ Stuurman, Nico, Susanne Heins and Ueli Aebi (1998). "Nuclear Lamins: Their Structure, Assembly, and Interactions". Journal of Strucutral Biology (122): 42-66. 18. PMID 9724605. 9 . ^ Goldman, A.E., Moir, R. D., Montag, L. M., Stewart, 19. M., and Goldman, R. D (1992). "Pathway of incorporation of microinjected lamin A into the nuclear envelope". Journal of Cell Biology (119): 725-732. PMID 1429833. 20. 10. ^ a b c d e Goldman, Robert D., Yosef Gruenbaum, Robert D. Moir, Dale K. Shumaker and Timothy P. Spann (2002). "Nuclear lamins: building blocks of nuclear architecture". 21. Genes & Dev. (16): 533-547. DOI:10.1101/gad.960502 (http://dx.doi.org/10.1101/gad.960502) . 11. ^ Ehrenhofer-Murray, Ann E. (June 2004). "Chromatin dynamics at DNA replication, transcription and repair". 22. European Journal of Biochemistry 271 (12): 2335. DOI:10.1111/j.1432-1033.2004.04162.x (http://dx.doi.org/10.1111/j.1432-1033.2004.04162.x) . 12. ^ Schardin, Margit, T. Cremer, H. D. Hager, M. Lang (Dec 1985). "Specific staining of human chromosomes in 23. Chinese hamster x man hybrid cell lines demonstrates interphase chromosome territories (http://www.springerlink.com/content/lv101t8w17306071/)24. ". Human Genetics 71 (4): 281-287. DOI:10.1007/BF00388452 (http://dx.doi.org/10.1007/BF00388452) . PMID 25. 2416668. 11 of 13 ^ Lamond, Angus I., William C. Earnshaw (24 April 1998). "Structure and Function in the Nucleus". Science 280: 547-553. PMID 9554838. ^ Kurz, A, S Lampel, JE Nickolenko, J Bradl, A Benner, RM Zirbel, T Cremer and P Lichter (1996). "Active and inactive genes localize preferentially in the periphery of chromosome territories (http://intl.jcb.org/cgi/content/abstract/135/5/1195) ". The Journal of Cell Biology 135: 1195-1205. PMID 8947544. ^ Hernandez-Verdun, Danie`le (2006). "Nucleolus: from structure to dynamics". Histochem. Cell. Biol (125): 127-137. DOI:10.1007/s00418-005-0046-4 (http://dx.doi.org/10.1007/s00418-005-0046-4) . ^ a b Lamond, Angus I., Judith E. Sleeman. "Nuclear substructure and dynamics". Current Biology 13 (21): R825-8. PMID 14588256. ^ a b c Cioce, Mario, William C. Earnshaw (2005). "Cajal Bodies: A Long History of Discovery". Annual Review of Cell and Developmental Biology 21: 105-131. DOI:0.1146/annurev.cellbio.20.010403.103738 (http://dx.doi.org/0.1146/annurev.cellbio.20.010403.103738 . ^ a b c Pollard, Thomas D., William C. Earnshaw (2004). Cell Biology. Philadelphia: Saunders. ISBN 0721633609. ^ a b c Dundr, Miroslav, Tom Misteli (2001). "Functional architecture in the cell nucleus". Biochem. J. (356): 297-310. PMID 11368755. ^ Matera, A. Gregory (1998). "Of Coiled Bodies, Gems, and Salmon". Journal of Cellular Biochemistry (70): 181–192. PMID 9671224. ^ Goebel, H.H., I Warlow (January 1997). "Nemaline myopathy with intranuclear rods--intranuclear rod myopathy". Neuromuscular Disorders 7 (1): 13-19. PMID 9132135. ^ Handwerger, Korie E., Joseph G. Gall (January 2006). "Subnuclear organelles: new insights into form and function". TRENDS in Cell Biology 16 (1): 19-26. DOI:10.1016/j.tcb.2005.11.005 (http://dx.doi.org/10.1016/j.tcb.2005.11.005) . ^ Lehninger, Albert L., David L. Nelson, Michael M. Cox. (2000). Lehninger principles of biochemistry, 3rd, New York: Worth Publishers. ISBN 1572599316. ^ Görlich, Dirk, Ulrike Kutay (1999). "Transport between the cell nucleus and the cytoplasm". Ann. Rev. Cell Dev. Biol. (15): 607-660. PMID 10611974. ^ Watson, JD, Baker TA, Bell SP, Gann A, Levine M, Losick R. (2004). “Ch9-10”, Molecular Biology of the 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia Gene, 5th ed., Peason Benjamin Cummings; CSHL Press.. 26. ^ Lippincott-Schwartz, Jennifer (7 March 2002). "Cell biology: Ripping up the nuclear envelope". Nature 416 (6876): 31-32. DOI:10.1038/416031a (http://dx.doi.org/10.1038/416031a) . 27. ^ Skutelsky, E., Danon D. (June 1970). "Comparative study of nuclear expulsion from the late erythroblast and cytokinesis". J Cell Biol (60(3)): 625-35. PMID 5422968. 28. ^ Torous, DK, Dertinger SD, Hall NE, Tometsko CR. (2000). "Enumeration of micronucleated reticulocytes in rat peripheral blood: a flow cytometric study". Mutat Res (465(1-2)): 91-9. PMID 10708974. 29. ^ Hutter, KJ, Stohr M. (1982). "Rapid detection of mutagen induced micronucleated erythrocytes by flow cytometry". Histochemistry (75(3)): 353-62. PMID 7141888. 30. ^ Zettler, LA, Sogin ML, Caron DA (1997). "Phylogenetic relationships between the Acantharea and the Polycystinea: A molecular perspective on Haeckel's Radiolaria". Proc Natl Acad Sci USA (94): 11411-11416. PMID 9326623. 31. ^ Horton, TR (2006). "The number of nuclei in basidiospores of 63 species of ectomycorrhizal Homobasidiomycetes". Mycologia (98(2)): 233-8. PMID 16894968. 32. ^ McInnes, A, Rennick DM (1988). "Interleukin 4 induces cultured monocytes/macrophages to form giant multinucleated cells". J Exp Med (167): 598-611. PMID 3258008. http://en.wikipedia.org/wiki/Cell_nucleus 33. ^ Goldring, SR, Roelke MS, Petrison KK, Bhan AK (1987). "Human giant cell tumors of bone identification and characterization of cell types". J Clin Invest (79(2)): 483–491. PMID 3027126. 34. ^ Pennisi E. (2004). "Evolutionary biology. The birth of the nucleus". Science 305 (5685): 766-8.. PMID 15297641. 35. ^ Lopez-Garcia P, Moreira D. (2006). "Selective forces for the origin of the eukaryotic nucleus". Bioessays 28 (5): 525-33. PMID 16615090. 36. ^ Fuerst JA. (2005). "Intracellular compartmentation in planctomycetes.journal = Annu Rev Microbiol.." 59: 299-328. PMID 15910279. 37. ^ Hartman H, Fedorov A. (2002). "The origin of the eukaryotic cell: a genomic investigation". Proc Natl Acad Sci U S A. 99 (3): 1420-5. PMID 11805300. 38. ^ Bell PJ. (2001). Viral eukaryogenesis: was the ancestor of the nucleus a complex DNA virus? J Mol Biol Sep;53(3):251-6. 39. ^ Takemura M. (2001). Poxviruses and the origin of the eukaryotic nucleus. J Mol Evol 52(5):419-25. 40. ^ Villareal LP, DeFilippis VR. (2000). A hypothesis for DNA viruses as the origin of eukaryotic replication proteins. J Virol 74(15):7079-84. 41. ^ Bell PJ. (2006). Sex and the eukaryotic cell cycle is consistent with a viral ancestry for the eukaryotic nucleus. J Theor Biol Epub before print. 42. ^ de Roos AD (2006). "The origin of the eukaryotic cell based on conservation of existing interfaces". Artif Life 12 (4): 513-23.. PMID 16953783. Further reading Goldman, Robert D., Yosef Gruenbaum, Robert D. Moir, Dale K. Shumaker and Timothy P. Spann (2002). "Nuclear lamins: building blocks of nuclear architecture". Genes & Dev. (16): 533-547. DOI:10.1101/gad.960502 (http://dx.doi.org/10.1101/gad.960502) . A review article about nuclear lamins, explaining their structure and various roles Görlich, Dirk, Ulrike Kutay (1999). "Transport between the cell nucleus and the cytoplasm". Ann. Rev. Cell Dev. Biol. (15): 607-660. PMID 10611974. A review article about nuclear transport, explains the principles of the mechanism, and the various transport pathways Lamond, Angus I., William C. Earnshaw (24 APRIL 1998). "Structure and Function in the Nucleus". Science 280: 547-553. PMID 9554838. A review article about the nucleus, explaining the structure of chromosomes within the organelle, and describing the nucleolus and other subnuclear bodies Pennisi E. (2004). "Evolutionary biology. The birth of the nucleus". Science 305 (5685): 766-8.. PMID 15297641. A review article about the evolution of the nucleus, explaining a number of different theories Pollard, Thomas D., William C. Earnshaw (2004). Cell Biology. Philadelphia: Saunders. ISBN 0721633609. 12 of 13 23/11/06 15:09 Cell nucleus - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Cell_nucleus A university level textbook focusing on cell biology. Contains information on nucleus structure and function, including nuclear transport, and subnuclear domains External links cellnucleus.com (http://www.cellnucleus.com/education_main.htm) Website covering structure and function of the nucleus from the Department of Oncology at the University of Alberta. The Nuclear Protein Database (http://npd.hgu.mrc.ac.uk/compartments.html) Information on nuclear components. The Nucleus Collection (http://cellimages.ascb.org/cdm4/browse.php?CISOROOT=/p4041coll6) in the Image & Video Library (http://cellimages.ascb.org/) of The American Society for Cell Biology (http://www.ascb.org/) contains peer-reviewed still images and video clips that illustrate the nucleus. Nuclear Envelope and Nuclear Import Section (http://cellimages.ascb.org/u?/p4041coll11,62) from Landmark Papers in Cell Biology (http://cellimages.ascb.org/cdm4/browse.php?CISOROOT=%2Fp4041coll11) , Joseph G. Gall, J. Richard McIntosh, eds., contains digitized commentaries and links to seminal research papers on the nucleus. Published online in the Image & Video Library (http://cellimages.ascb.org/) of The American Society for Cell Biology (http://www.ascb.org/) Organelles of the cell Acrosome | Cell wall | Cell membrane | Chloroplast | Cilium/Flagellum | Centrosome | Cytoplasm | Endoplasmic reticulum | Endosome | Golgi apparatus | Lysosome | Melanosome | Mitochondrion | Myofibril | Nucleus | Nucleolus (sub-organelle, found within the nucleus) | Parenthesome | Peroxisome | Plastid | Ribosome | Vacuole | Vesicle Retrieved from "http://en.wikipedia.org/wiki/Cell_nucleus" Categories: Organelles | Medical terms This page was last modified 05:19, 20 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 13 of 13 23/11/06 15:09 Reading(s) #6 Genetics/Introduction - Wikibooks, collection of open-content textbooks http://en.wikibooks.org/wiki/Genetics/Introduction Genetics/Introduction From Wikibooks, the open-content textbooks collection < Genetics Genetics, study of the function and behavior of genes. Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans. Offspring receive a mixture of genetic information from both parents. This process contributes to the great variation of traits that we see in nature, such as the color of a flower’s petals, the markings on a butterfly’s wings, or such human behavioral traits as personality or musical talent. Geneticists seek to understand how the information encoded in genes is used and controlled by cells and how it is transmitted from one generation to the next. Geneticists also study how tiny variations in genes can disrupt an organism’s development or cause disease. Increasingly, modern genetics involves genetic engineering, a technique used by scientists to manipulate genes. Genetic engineering has produced many advances in medicine and industry, but the potential for abuse of this technique has also presented society with many ethical and legal controversies. Genetic information is encoded and transmitted from generation to generation in deoxyribonucleic acid (DNA). DNA is a coiled molecule organized into structures called chromosomes within cells. Segments along the length of a DNA molecule form genes. Genes direct the synthesis of proteins, the molecular laborers that carry out all life-supporting activities in the cell. Although all humans share the same set of genes, individuals can inherit different forms of a given gene, making each person genetically unique. Since the earliest days of plant and animal domestication, around 10,000 years ago, humans have understood that characteristic traits of parents could be transmitted to their offspring. The first to speculate about how this process worked were Greek scholars around the 4th century bc, who promoted theories based on conjecture or superstition. Some of these theories remained in favor for several centuries. The scientific study of genetics did not begin until the late 19th century. In experiments with garden peas, Austrian monk Gregor Mendel described the patterns of inheritance, observing that traits were inherited as separate units. These units are now known as genes. Mendel’s work formed the foundation for later scientific achievements that heralded the era of modern genetics. Most of the discoveries about genes and DNA happened after Charles Darwin 1859 famous book on The Origin of Species by Means of Natural Selection, or the preservation of favoured races in the struggle for life. Retrieved from "http://en.wikibooks.org/wiki/Genetics/Introduction" Category: Genetics This page was last modified 22:00, 15 November 2006. All text is available under the terms of the GNU Free Documentation License (see Copyrights for details). Wikibooks® is a registered trademark of the Wikimedia Foundation, Inc. Privacy policy About Wikibooks Disclaimers 1 of 1 23/11/06 15:09 Reading(s) #7 Reading(s) #7.1 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... INTRODUCTION TO GENETICS Table of Contents Heredity, historical perspectives | The Monk and his peas | Principle of segregation Dihybrid Crosses | Mutations | Genetic Terms | Links Heredity, Historical Perspective | Back to Top For much of human history people were unaware of the scientific details of how babies were conceived and how heredity worked. Clearly they were conceived, and clearly there was some hereditary connection between parents and children, but the mechanisms were not readily apparent. The Greek philosophers had a variety of ideas: Theophrastus proposed that male flowers caused female flowers to ripen; Hippocrates speculated that "seeds" were produced by various body parts and transmitted to offspring at the time of conception, and Aristotle thought that male and female semen mixed at conception. Aeschylus, in 458 BC, proposed the male as the parent, with the female as a "nurse for the young life sown within her". During the 1700s, Dutch microscopist Anton van Leeuwenhoek (1632-1723) discovered "animalcules" in the sperm of humans and other animals. Some scientists speculated they saw a "little man" (homunculus) inside each sperm. These scientists formed a school of thought known as the "spermists". They contended the only contributions of the female to the next generation were the womb in which the homunculus grew, and prenatal influences of the womb. An opposing school of thought, the ovists, believed that the future human was in the egg, and that sperm merely stimulated the growth of the egg. Ovists thought women carried eggs containing boy and girl children, and that the gender of the offspring was determined well before conception. Pangenesis was an idea that males and females formed "pangenes" in every organ. These pangenes subsequently moved through their blood to the genitals and then to the children. The concept originated with the ancient Greeks and influenced biology until little over 100 years ago. The terms "blood relative", "full-blooded", and "royal blood" are relicts of pangenesis. Francis Galton, Charles Darwin's cousin, experimentally tested and disproved pangenesis during the 1870s. Blending theories of inheritance supplanted the spermists and ovists during the 19th century. The mixture of sperm and egg resulted in progeny that were a "blend" of two parents' characteristics. Sex cells are known collectively as gametes (gamos, Greek, meaning marriage). According to the blenders, when a black furred animal mates with white furred animal, you would expect all resulting progeny would be gray (a color intermediate between black and white). This is often not the case. Blending theories ignore characteristics skipping a generation. Charles Darwin had to deal with the implications of blending in his theory of evolution. He was forced to recognize blending as not important (or at least not the major principle), and suggest that science 1 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... of the mid-1800s had not yet got the correct answer. That answer came from a contemporary, Gregor Mendel, although Darwin apparently never knew of Mendel's work. The Monk and his peas | Back to Top An Austrian monk, Gregor Mendel, developed the fundamental principles that would become the modern science of genetics. Mendel demonstrated that heritable properties are parceled out in discrete units, independently inherited. These eventually were termed genes. Gregor Mendel, the Austrian monk who figured out the rules of hereity. The above photo is from http://www.open.cz/project/tourist/person/photo.htm. Mendel reasoned an organism for genetic experiments should have: 1. a number of different traits that can be studied 2. plant should be self-fertilizing and have a flower structure that limits accidental contact 3. offspring of self-fertilized plants should be fully fertile. Mendel's experimental organism was a common garden pea (Pisum sativum), which has a flower that lends itself to self-pollination. The male parts of the flower are termed the anthers. They produce pollen, which contains the male gametes (sperm). The female parts of the flower are the stigma, style, and ovary. The egg (female gamete) is produced in the ovary. The process of pollination (the transfer of pollen from anther to stigma) occurs prior to the opening of the pea flower. The pollen grain grows a pollen tube which allows the sperm to travel through the stigma and style, eventually reaching the ovary. The ripened ovary wall becomes the fruit (in this case the pea pod). Most flowers allow cross-pollination, which can be difficult to deal with in genetic studies if the male parent plant is not known. Since pea plants are self-pollinators, the genetics of the parent can be more easily understood. Peas are also self-compatible, allowing self-fertilized embryos to develop as readily as out-fertilized embryos. Mendel tested all 34 varieties of peas available to him through seed dealers. The garden peas were planted and studied for eight years. Each character studied had two distinct forms, such as tall or short plant height, or smooth or wrinkled seeds. 2 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... Mendel's experiments used some 28,000 pea plants. 3 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... Some of Mendel's traits as expressed in garden peas. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Mendel's contribution was unique because of his methodical approach to a definite problem, use of clear-cut variables and application of mathematics (statistics) to the problem. Gregor Using pea plants and statistical methods, Mendel was able to demonstrate that traits were passed from each parent to their offspring through the inheritance of genes. Mendel's work showed: 4 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... 1. Each parent contributes one factor of each trait shown in offspring. 2. The two members of each pair of factors segregate from each other during gamete formation. 3. The blending theory of inheritance was discounted. 4. Males and females contribute equally to the traits in their offspring. 5. Acquired traits are not inherited. Principle of Segregation | Back to Top Mendel studied the inheritance of seed shape first. A cross involving only one trait is referred to as a monohybrid cross. Mendel crossed pure-breeding (also referred to as true-breeding) smooth-seeded plants with a variety that had always produced wrinkled seeds (60 fertilizations on 15 plants). All resulting seeds were smooth. The following year, Mendel planted these seeds and allowed them to self-fertilize. He recovered 7324 seeds: 5474 smooth and 1850 wrinkled. To help with record keeping, generations were labeled and numbered. The parental generation is denoted as the P1 generation. The offspring of the P1 generation are the F1 generation (first filial). The self-fertilizing F1 generation produced the F2 generation (second filial). Inheritance of two alleles, S and s, in peas. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. 5 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... Punnett square explaining the behavior of the S and s alleles. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. P1: smooth X wrinkled F1 : all smooth F2 : 5474 smooth and 1850 wrinkled Meiosis, a process unknown in Mendel's day, explains how the traits are inherited. 6 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... The inheritance of the S and s alleles explained in light of meiosis. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Mendel studied seven traits which appeared in two discrete forms, rather than continuous characters which are often difficult to distinguish. When "true-breeding" tall plants were crossed with "true-breeding" short plants, all of the offspring were tall plants. The parents in the cross were the P1 generation, and the offspring represented the F1 generation. The trait referred to as tall was considered dominant, while short was recessive. Dominant traits were defined by Mendel as those which appeared in the F1 generation in crosses between true-breeding strains. Recessives were those which "skipped" a generation, being expressed only when the dominant trait is absent. Mendel's plants exhibited complete dominance, in which the phenotypic expression of alleles was either dominant or recessive, not "in between". When members of the F1 generation were crossed, Mendel recovered mostly tall offspring, with some short ones also occurring. Upon statistically analyzing the F2 7 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... generation, Mendel determined the ratio of tall to short plants was approximately 3:1. Short plants have skipped the F1 generation, and show up in the F2 and succeeding generations. Mendel concluded that the traits under study were governed by discrete (separable) factors. The factors were inherited in pairs, with each generation having a pair of trait factors. We now refer to these trait factors as alleles. Having traits inherited in pairs allows for the observed phenomena of traits "skipping" generations. Summary of Mendel's Results: 1. The F1 offspring showed only one of the two parental traits, and always the same trait. 2. Results were always the same regardless of which parent donated the pollen (was male). 3. The trait not shown in the F1 reappeared in the F2 in about 25% of the offspring. 4. Traits remained unchanged when passed to offspring: they did not blend in any offspring but behaved as separate units. 5. Reciprocal crosses showed each parent made an equal contribution to the offspring. Mendel's Conclusions: 1. Evidence indicated factors could be hidden or unexpressed, these are the recessive traits. 2. The term phenotype refers to the outward appearance of a trait, while the term genotype is used for the genetic makeup of an organism. 3. Male and female contributed equally to the offsprings' genetic makeup: therefore the number of traits was probably two (the simplest solution). 4. Upper case letters are traditionally used to denote dominant traits, lower case letters for recessives. Mendel reasoned that factors must segregate from each other during gamete formation (remember, meiosis was not yet known!) to retain the number of traits at 2. The Principle of Segregation proposes the separation of paired factors during gamete formation, with each gamete receiving one or the other factor, usually not both. Organisms carry two alleles for every trait. These traits separate during the formation of gametes. A hypertext version (in German or English, annotated also available) of Mendel's 1865 paper is available by clicking here. Dihybrid Crosses | Back to Top When Mendel considered two traits per cross (dihybrid, as opposed to single-trait-crosses, monohybrid), The resulting (F2) generation did not have 3:1 dominant:recessive phenotype ratios. The two traits, if considered to inherit independently, fit into the principle of segregation. Instead of 4 possible genotypes from a monohybrid cross, dihybrid crosses have as many as 16 possible genotypes. 8 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... Mendel realized the need to conduct his experiments on more complex situations. He performed experiments tracking two seed traits: shape and color. A cross concerning two traits is known as a dihybrid cross. Crosses With Two Traits Smooth seeds (S) are dominant over wrinkled (s) seeds. Yellow seed color (Y) is dominant over green (g). Inheritance of two traits simultaneously, a dihybrid cross. The above graphic is from the Genetics pages at McGill University (http://www.mcgill.ca/nrs/dihyb2.gif). Again, meiosis helps us understand the behavior of alleles. 9 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... The inheritance of two traits on different chromosomes can be explained by meiosis. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Methods, Results, and Conclusions Mendel started with true-breeding plants that had smooth, yellow seeds and crossed them with true-breeding plants having green, wrinkled seeds. All seeds in the F1 had smooth yellow seeds. The F2 plants self-fertilized, and produced four phenotypes: 315 smooth yellow 108 smooth green 101 wrinkled yellow 32 wrinkled green Mendel analyzed each trait for separate inheritance as if the other trait were not 10 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... present.The 3:1 ratio was seen separately and was in accordance with the Principle of Segregation. The segregation of S and s alleles must have happened independently of the segregation of Y and y alleles. The chance of any gamete having a Y is 1/2; the chance of any one gamete having a S is 1/2.The chance of a gamete having both Y and S is the product of their individual chances (or 1/2 X 1/2 = 1/4). The chance of two gametes forming any given genotype is 1/4 X 1/4 (remember, the product of their individual chances). Thus, the Punnett Square has 16 boxes. Since there are more possible combinations to produce a smooth yellow phenotype (SSYY, SsYy, SsYY, and SSYy), that phenotype is more common in the F2. From the results of the second experiment, Mendel formulated the Principle of Independent Assortment -- that when gametes are formed, alleles assort independently. If traits assort independent of each other during gamete formation, the results of the dihybrid cross can make sense. Since Mendel's time, scientists have discovered chromosomes and DNA. We now interpret the Principle of Independent Assortment as alleles of genes on different chromosomes are inherited independently during the formation of gametes. This was not known to Mendel. Punnett squares deal only with probability of a genotype showing up in the next generation. Usually if enough offspring are produced, Mendelian ratios will also be produced. Step 1 - definition of alleles and determination of dominance. Step 2 - determination of alleles present in all different types of gametes. Step 3 - construction of the square. Step 4 - recombination of alleles into each small square. Step 5 - Determination of Genotype and Phenotype ratios in the next generation. Step 6 - Labeling of generations, for example P1, F1, etc. While answering genetics problems, there are certain forms and protocols that will make unintelligible problems easier to do. The term "true-breeding strain" is a code word for homozygous. Dominant alleles are those that show up in the next generation in crosses between two different "true-breeding strains". The key to any genetics problem is the recessive phenotype (more properly the phenotype that represents the recessive genotype). It is that organism whose genotype can be determined by examination of the phenotype. Usually homozygous dominant and heterozygous individuals have identical phenotypes (although their genotypes are different). This becomes even more important in dihybrid crosses. Mutations | Back to Top Hugo de Vries, one of three turn-of-the-century scientists who rediscovered the work of Mendel, recognized that occasional abrupt, sudden changes occurred in the patterns 11 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... of inheritance in the primrose plant. These sudden changes he termed mutations. De Vries proposed that new alleles arose by mutations. Charles Darwin, in his Origin of Species, was unable to describe how heritable changes were passed on to subsequent generations, or how new adaptations arose. Mutations provided answers to problems of the appearance of novel adaptations. The patterns of Mendelian inheritance explained the perseverance of rare traits in organisms, all of which increased variation, as you recall that was a major facet of Darwin's theory. Mendel's work was published in 1866 but not recognized until the early 1900s when three scientists independently verified his principles, more than twenty years after his death. Ignored by the scientific community during his lifetime, Mendel's work is now a topic enjoyed by generations of biology students (;)) Genetic Terms | Back to Top Definitions of terms. While we are discussing Mendel, we need to understand the context of his times as well as how his work fits into the modern science of genetics. Gene - a unit of inheritance that usually is directly responsible for one trait or character. Allele - an alternate form of a gene. Usually there are two alleles for every gene, sometimes as many a three or four. Homozygous - when the two alleles are the same. Heterozygous - when the two alleles are different, in such cases the dominant allele is expressed. Dominant - a term applied to the trait (allele) that is expressed irregardless of the second allele. Recessive - a term applied to a trait that is only expressed when the second allele is the same (e.g. short plants are homozygous for the recessive allele). Phenotype - the physical expression of the allelic composition for the trait under study. Genotype - the allelic composition of an organism. Punnett squares - probability diagram illustrating the possible offspring of a mating. Links | Back to Top History of Genetics Web Pages (University of California, Davis) Quantitative Genetics Resources (University of Arizona) MendelWeb Hey, how many folks have their own webpages over a century after their deaths? Classic Papers in Genetics These files are downloadable in Adobe Acrobat format. The site has a link to get the viewer from Adobe. 12 of 13 23/11/06 15:10 Intro to Genetics http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookgenint... Mendelian Genetics (Bio 181 at the University of Arizona) Lecture notes, a genetics tutorial, and some very nice graphics. Monohybrid Problem Set (The Biology Project, U of AZ) Tutorial on single-trait crosses. Dihybrid Problem Set (The Biology Project, U of AZ) Tutorial on two-trait crosses. The Virtual Fly Lab Conduct online genetics crosses with virtual Drosophila. An excellent, much cited and visited site. MIT Hypertextbook Chapter on Mendelain Genetics The History of Genetics (Whitman College) An outline. Course Outline in Genetics (McGill University) An outline and many quality graphics and animations. Interactive Pea Experiment (Bill Kendrick) Select peas to breed. Nice introduction to genetics experiments. Glossary of Genetics Terms Text ©1992, 1994, 1997, 1999, 2000, 2001, by M.J. Farabee, all rights reserved. Use for educational purposes is encouraged. Back to Table of Contents | Go to GENE INTERACTIONS Email: mj.farabee@emcmail.maricopa.edu Last modified: The URL of this page is: 13 of 13 23/11/06 15:10 Reading(s) #7.2 Genetics/Mendelian Inheritence - Wikibooks, collection of open-cont... http://en.wikibooks.org/wiki/Genetics/Mendelian_Inheritence#Introdu... Genetics/Mendelian Inheritence From Wikibooks, the open-content textbooks collection < Genetics Introduction Gregor Johann Mendel was a monk in the Augustinian Monastery in the Brunn, Czech Republic. In 1854 he began the experiments which started modern genetics. His work with garden peas, Pisum sativum, was vital to our understanding of inheritance. He is known as the Father Of Genetics. Mendel's Experiment Mendel's first step was breeding pure breeding strains of peas. The traits he studied included: Pea colour Height and whether the Peas were wrinkled or smooth. Mendel crossed the pure breeding Parental Generation (designated P). He found that the first generation (F1) was exclusively phenotypically one of the parental types. Mendel then crossed his F1 generation with itself. He found that the F2 generation showed a surprising trait, three quarters were like the F1 generation, while the remaining quarter were like the other Parents. From this Mendel realised that there were two versions of each loci, one of which expressed dominance over the other. He called this Biparticulate Inheritance. If a gene was following this 3:1 pattern it was said to be segregating Normally. By looking at multiple genes, Mendel showed that they were not linked to each other and that each loci he studied had no influence over the others. He called this Independent assortment. By studying cases where the Mendelian laws we can also learn a lot. For instance, if a gene isn't segragating normally it may be sex linked. If two genes aren't Assorting Independantly they're probably on the same chromosome Mendel's laws are the first step to understanding Genetics, they lay down the basic concept of inheritance. Retrieved from "http://en.wikibooks.org/wiki/Genetics/Mendelian_Inheritence" Category: Genetics This page was last modified 19:03, 2 July 2006. All text is available under the terms of the GNU Free Documentation License (see Copyrights for details). Wikibooks® is a registered trademark of the Wikimedia Foundation, Inc. Privacy policy About Wikibooks Disclaimers 1 of 1 23/11/06 15:12 Reading(s) #8 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html CELL DIVISION: BINARY FISSION AND MITOSIS Table of Contents The Cell Cycle | Prokaryotic Cell Division | Eukaryotic Cell Division | Mitosis Prophase | Metaphase | Anaphase | Telophase | Cytokinesis | Links The Cell Cycle | Back to Top Despite differences between prokaryotes and eukaryotes, there are several common features in their cell division processes. Replication of the DNA must occur. Segregation of the "original" and its "replica" follow. Cytokinesis ends the cell division process. Whether the cell was eukaryotic or prokaryotic, these basic events must occur. Cytokinesis is the process where one cell splits off from its sister cell. It usually occurs after cell division. The Cell Cycle is the sequence of growth, DNA replication, growth and cell division that all cells go through. Beginning after cytokinesis, the daughter cells are quite small and low on ATP. They acquire ATP and increase in size during the G1 phase of Interphase. Most cells are observed in Interphase, the longest part of the cell cycle. After acquiring sufficient size and ATP, the cells then undergo DNA Synthesis (replication of the original DNA molecules, making identical copies, one "new molecule" eventually destined for each new cell) which occurs during the S phase. Since the formation of new DNA is an energy draining process, the cell undergoes a second growth and energy acquisition stage, the G2 phase. The energy acquired during G2 is used in cell division (in this case mitosis). 1 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html The cell cycle. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Regulation of the cell cycle is accomplished in several ways. Some cells divide rapidly (beans, for example take 19 hours for the complete cycle; red blood cells must divide at a rate of 2.5 million per second). Others, such as nerve cells, lose their capability to divide once they reach maturity. Some cells, such as liver cells, retain but do not normally utilize their capacity for division. Liver cells will divide if part of the liver is removed. The division continues until the liver reaches its former size. Cancer cells are those which undergo a series of rapid divisions such that the daughter cells divide before they have reached "functional maturity". Environmental factors such as changes in temperature and pH, and declining nutrient levels lead to declining cell division rates. When cells stop dividing, they stop usually at a point late in the G1 phase, the R point (for restriction). Prokaryotic Cell Division | Back to Top Prokaryotes are much simpler in their organization than are eukaryotes. There are a great many more organelles in eukaryotes, also more chromosomes. The usual method of prokaryote cell division is termed binary fission. The prokaryotic chromosome is a single DNA molecule that first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart, the replicate and original chromosomes are separated. Following cell splitting (cytokinesis), there are then two cells of identical genetic composition (except for the rare chance of a spontaneous mutation). This animated GIF of binary fission is from: http://www.slic2.wsu.edu:82/hurlbert/micro101/pages/Chap2.html#two_bact_groups The prokaryote chromosome is much easier to manipulate than the eukaryotic one. We thus know much more about the location of genes and their control in prokaryotes. One consequence of this asexual method of reproduction is that all organisms in a colony are genetic equals. When treating a bacterial disease, a drug that kills one bacteria (of a specific type) will also kill all other members of that clone (colony) it comes in contact with. 2 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html Rod-Shaped Bacterium, E. coli, dividing by binary fission (TEM x92,750). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. 3 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html Rod-Shaped Bacterium, hemorrhagic E. coli, strain 0157:H7 (division) (SEM x22,810). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Eukaryotic Cell Division | Back to Top Due to their increased numbers of chromosomes, organelles and complexity, eukaryote cell division is more complicated, although the same processes of replication, segregation, and cytokinesis still occur. Mitosis | Back to Top Mitosis is the process of forming (generally) identical daughter cells by replicating and dividing the original chromosomes, in effect making a cellular xerox. Commonly the two processes of cell division are confused. Mitosis deals only with the segregation of the chromosomes and organelles into daughter cells. Click here to view an animated GIF of mitosis from http://www.biology.uc.edu/vgenetic/mitosis/mitosis.htm. Eukaryotic chromosomes occur in the cell in greater numbers than prokaryotic chromosomes. The condensed replicated chromosomes have several points of interest. The kinetochore is the point where microtubules of the spindle apparatus attach. Replicated chromosomes consist of two molecules of DNA (along with their associated histone proteins) known as chromatids. The area where both chromatids are in contact with each other is known as the centromere the kinetochores are on the outer sides of the centromere. Remember that chromosomes are condensed chromatin (DNA plus histone proteins). Structure of a eukaryotic chromosome. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. During mitosis replicated chromosomes are positioned near the middle of the 4 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html cytoplasm and then segregated so that each daughter cell receives a copy of the original DNA (if you start with 46 in the parent cell, you should end up with 46 chromosomes in each daughter cell). To do this cells utilize microtubules (referred to as the spindle apparatus) to "pull" chromosomes into each "cell". The microtubules have the 9+2 arrangement discussed earlier. Animal cells (except for a group of worms known as nematodes) have a centriole. Plants and most other eukaryotic organisms lack centrioles. Prokaryotes, of course, lack spindles and centrioles; the cell membrane assumes this function when it pulls the by-then replicated chromosomes apart during binary fission. Cells that contain centrioles also have a series of smaller microtubules, the aster, that extend from the centrioles to the cell membrane. The aster is thought to serve as a brace for the functioning of the spindle fibers. Structure and main features of a spindle apparatus. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. The phases of mitosis are sometimes difficult to separate. Remember that the process is a dynamic one, not the static process displayed of necessity in a textbook. Prophase | Back to Top Prophase is the first stage of mitosis proper. Chromatin condenses (remember that chromatin/DNA replicate during Interphase), the nuclear envelope dissolves, centrioles (if present) divide and migrate, kinetochores and kinetochore fibers form, and the spindle forms. 5 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html Pea Plant Nuclear DNA, from Vicea faba (TEM x105,000). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. 6 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html The events of Prophase. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Metaphase | Back to Top Metaphase follows Prophase. The chromosomes (which at this point consist of chromatids held together by a centromere) migrate to the equator of the spindle, where the spindles attach to the kinetochore fibers. Anaphase | Back to Top Anaphase begins with the separation of the centromeres, and the pulling of chromosomes (we call them chromosomes after the centromeres are separated) to opposite poles of the spindle. 7 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html The events of Metaphase and Anaphase. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Telophase | Back to Top Telophase is when the chromosomes reach the poles of their respective spindles, the nuclear envelope reforms, chromosomes uncoil into chromatin form, and the nucleolus (which had disappeared during Prophase) reform. Where there was one cell there are now two smaller cells each with exactly the same genetic information. These cells may then develop into different adult forms via the processes of development. The events of Telophase. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with 8 of 9 23/11/06 15:13 CELL DIVISION: BINARY FISSION AND MITOSIS http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html permission. Cytokinesis | Back to Top Cytokinesis is the process of splitting the daughter cells apart. Whereas mitosis is the division of the nucleus, cytokinesis is the splitting of the cytoplasm and allocation of the golgi, plastids and cytoplasm into each new cell. Links | Back to Top Access Excellence page on Mitosis Cell Division and the Cell Cycle (University of Alberta): Similar to this page, but with its own glossary and questions. Amoeba Proteus Mitosis Small photomicrographs of protistan mitosis. Cell Reproduction Notes from University of Georgia, plus some cool graphics of mitosis. Phases of Mitosis U Texas QuickTime® movies of mitosis. Animated Mitosis Yale University, a simplified series of cartoons about mitosis. Mitosis U Southern Mississippi, Grayscale drawings and photomicrographs of mitosis stages. Mitosis San Diego State U, shocked animation of the process. You will need the Shockwave plugin to view. If you don't have it, you can download it from them. McGill University Mitosis Page Quality site, with photos and downloadable animation and video. Comparison of Mitosis and Meiosis Whitman College, table summarizing each process. Whitefish Mitosis Review Cornell, photomicrographs of mitosis in whitefish. A nice review after lab! Part of a more extensive page of Cell Division Tutorials. Virtual Mitosis University of Cincinnati, Animated GIF and text about the stages of mitosis. Text ©1992, 1994, 1997, 1998, 2000, 2001, by M.J. Farabee, all rights reserved. Use for educational purposes is encouraged. Back to Table of Contents | MEIOSIS AND SEXUAL REPRODUCTION Email: mj.farabee@emcmail.maricopa.edu Last modified: The URL of this page is: 9 of 9 23/11/06 15:13 Reading(s) #9 Reading(s) #9.1 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... CELL DIVISION: MEIOSIS AND SEXUAL REPRODUCTION Table of Contents Meiosis | Ploidy | Life Cycles | Phases of Meiosis | Prophase I | Metaphase I Anaphase I | Telophase I | Prophase II | Metaphase II | Anaphase II | Telophase II Comparison of Mitosis and Meiosis | Gametogenesis | Links Meiosis | Back to Top Sexual reproduction occurs only in eukaryotes. During the formation of gametes, the number of chromosomes is reduced by half, and returned to the full amount when the two gametes fuse during fertilization. Ploidy | Back to Top Haploid and diploid are terms referring to the number of sets of chromosomes in a cell. Gregor Mendel determined his peas had two sets of alleles, one from each parent. Diploid organisms are those with two (di) sets. Human beings (except for their gametes), most animals and many plants are diploid. We abbreviate diploid as 2n. Ploidy is a term referring to the number of sets of chromosomes. Haploid organisms/cells have only one set of chromosomes, abbreviated as n. Organisms with more than two sets of chromosomes are termed polyploid. Chromosomes that carry the same genes are termed homologous chromosomes. The alleles on homologous chromosomes may differ, as in the case of heterozygous individuals. Organisms (normally) receive one set of homologous chromosomes from each parent. Meiosis is a special type of nuclear division which segregates one copy of each homologous chromosome into each new "gamete". Mitosis maintains the cell's original ploidy level (for example, one diploid 2n cell producing two diploid 2n cells; one haploid n cell producing two haploid n cells; etc.). Meiosis, on the other hand, reduces the number of sets of chromosomes by half, so that when gametic recombination (fertilization) occurs the ploidy of the parents will be reestablished. Most cells in the human body are produced by mitosis. These are the somatic (or vegetative) line cells. Cells that become gametes are referred to as germ line cells. The vast majority of cell divisions in the human body are mitotic, with meiosis being restricted to the gonads. Life Cycles | Back to Top Life cycles are a diagrammatic representation of the events in the organism's development and reproduction. When interpreting life cycles, pay close attention to the ploidy level of particular parts of the cycle and where in the life cycle meiosis 1 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... occurs. For example, animal life cycles have a dominant diploid phase, with the gametic (haploid) phase being a relative few cells. Most of the cells in your body are diploid, germ line diploid cells will undergo meiosis to produce gametes, with fertilization closely following meiosis. Plant life cycles have two sequential phases that are termed alternation of generations. The sporophyte phase is "diploid", and is that part of the life cycle in which meiosis occurs. However, many plant species are thought to arise by polyploidy, and the use of "diploid" in the last sentence was meant to indicate that the greater number of chromosome sets occur in this phase. The gametophyte phase is "haploid", and is the part of the life cycle in which gametes are produced (by mitosis of haploid cells). In flowering plants (angiosperms) the multicelled visible plant (leaf, stem, etc.) is sporophyte, while pollen and ovaries contain the male and female gametophytes, respectively. Plant life cycles differ from animal ones by adding a phase (the haploid gametophyte) after meiosis and before the production of gametes. Many protists and fungi have a haploid dominated life cycle. The dominant phase is haploid, while the diploid phase is only a few cells (often only the single celled zygote, as in Chlamydomonas ). Many protists reproduce by mitosis until their environment deteriorates, then they undergo sexual reproduction to produce a resting zygotic cyst. Phases of Meiosis | Back to Top Two successive nuclear divisions occur, Meiosis I (Reduction) and Meiosis II (Division). Meiosis produces 4 haploid cells. Mitosis produces 2 diploid cells. The old name for meiosis was reduction/ division. Meiosis I reduces the ploidy level from 2n to n (reduction) while Meiosis II divides the remaining set of chromosomes in a mitosis-like process (division). Most of the differences between the processes occur during Meiosis I. The above image is from http://www.biology.uc.edu/vgenetic/meiosis/ Prophase I | Back to Top Prophase I has a unique event -- the pairing (by an as yet undiscovered mechanism) of homologous chromosomes. Synapsis is the process of linking of the replicated homologous chromosomes. The resulting chromosome is termed a tetrad, being composed of two chromatids from each chromosome, forming a thick (4-strand) structure. Crossing-over may occur at this point. During crossing-over chromatids break and may be reattached to a different homologous chromosome. 2 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... The alleles on this tetrad: ABCDEFG ABCDEFG abcdefg abcdefg will produce the following chromosomes if there is a crossing-over event between the 2nd and 3rd chromosomes from the top: ABCDEFG ABcdefg abCDEFG abcdefg Thus, instead of producing only two types of chromosome (all capital or all lower case), four different chromosomes are produced. This doubles the variability of gamete genotypes. The occurrence of a crossing-over is indicated by a special structure, a chiasma (plural chiasmata) since the recombined inner alleles will align more with others of the same type (e.g. a with a, B with B). Near the end of Prophase I, the homologous chromosomes begin to separate slightly, although they remain attached at chiasmata. 3 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Crossing-over between homologous chromosomes produces chromosomes with new associations of genes and alleles. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Events of Prophase I (save for synapsis and crossing over) are similar to those in Prophase of mitosis: chromatin condenses into chromosomes, the nucleolus dissolves, nuclear membrane is disassembled, and the spindle apparatus forms. 4 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Major events in Prophase I. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Metaphase I | Back to Top Metaphase I is when tetrads line-up along the equator of the spindle. Spindle fibers attach to the centromere region of each homologous chromosome pair. Other metaphase events as in mitosis. Anaphase I | Back to Top Anaphase I is when the tetrads separate, and are drawn to opposite poles by the spindle fibers. The centromeres in Anaphase I remain intact. Events in prophase and metaphse I. Image from Purves et al., Life: The Science of Biology, 4th 5 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Telophase I | Back to Top Telophase I is similar to Telophase of mitosis, except that only one set of (replicated) chromosomes is in each "cell". Depending on species, new nuclear envelopes may or may not form. Some animal cells may have division of the centrioles during this phase. The events of Telophase I. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Prophase II | Back to Top During Prophase II, nuclear envelopes (if they formed during Telophase I) dissolve, and spindle fibers reform. All else is as in Prophase of mitosis. Indeed Meiosis II is very similar to mitosis. 6 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... The events of Prophase II. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Metaphase II | Back to Top Metaphase II is similar to mitosis, with spindles moving chromosomes into equatorial area and attaching to the opposite sides of the centromeres in the kinetochore region. Anaphase II | Back to Top During Anaphase II, the centromeres split and the former chromatids (now chromosomes) are segregated into opposite sides of the cell. 7 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... The events of Metaphase II and Anaphase II. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Telophase II | Back to Top Telophase II is identical to Telophase of mitosis. Cytokinesis separates the cells. The events of Telophase II. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Comparison of Mitosis and Meiosis | Back to Top Mitosis maintains ploidy level, while meiosis reduces it. Meiosis may be considered a reduction phase followed by a slightly altered mitosis. Meiosis occurs in a relative few cells of a multicellular organism, while mitosis is more common. 8 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... 9 of 14 http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... 31/03/07 05:54 CELL DIVISION: Meiosis... 10 of 14 http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Comparison of the events in Mitosis and Meiosis. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Gametogenesis | Back to Top Gametogenesis is the process of forming gametes (by definition haploid, n) from diploid cells of the germ line. Spermatogenesis is the process of forming sperm cells by meiosis (in animals, by mitosis in plants) in specialized organs known as gonads (in males these are termed testes). After division the cells undergo differentiation to become sperm cells. Oogenesis is the process of forming an ovum (egg) by meiosis (in animals, by mitosis in the gametophyte in plants) in specialized gonads known as ovaries. Whereas in spermatogenesis all 4 meiotic products develop into gametes, oogenesis places most of the cytoplasm into the large egg. The other cells, the polar bodies, do not develop. This all the cytoplasm and organelles go into the egg. Human males produce 200,000,000 sperm per day, while the female produces one egg (usually) each menstrual cycle. 11 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Gametogenesis. Images from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates (www.sinauer.com) and WH Freeman (www.whfreeman.com), used with permission. Spermatogenesis Sperm production begins at puberty at continues throughout life, with several hundred million sperm being produced each day. Once sperm form they move into the epididymis, where they mature and are stored. 12 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Human Sperm (SEM x5,785). This image is copyright Dennis Kunkel at www.DennisKunkel.com, used with permission. Oogenesis The ovary contains many follicles composed of a developing egg surrounded by an outer layer of follicle cells. Each egg begins oogenesis as a primary oocyte. At birth each female carries a lifetime supply of developing oocytes, each of which is in Prophase I. A developing egg (secondary oocyte) is released each month from puberty until menopause, a total of 400-500 eggs. 13 of 14 31/03/07 05:54 CELL DIVISION: Meiosis... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeios... Oogenesis. The above image is from http://www.grad.ttuhsc.edu/courses/histo/notes/female.html. Links | Back to Top Access Excellence page on Mitosis Cell Division and the Cell Cycle (University of Alberta): Similar to this page, but with its own glossary and questions. Amoeba Proteus Mitosis Small photomicrographs of protistan mitosis. Animated Meiosis Yale University, a simplified series of cartoons about meiosis. Meiosis Tutorial North Carolina State University, animations and 3-D graphics. McGill University Mitosis Page Quality site, with photos and downloadable animation and video. Virtual Meiosis University of Cincinnati, Animated GIF and text/images to explain meiosis. Text ©1992, 1994, 1997, 1998, 2000, 2001, 2007, by M.J. Farabee, all rights reserved. Use for educational purposes is encouraged. Back to Table of Contents | Mitosis Page Email: mj.farabee@emcmail.maricopa.edu Last modified: The URL of this page is: 14 of 14 31/03/07 05:54 Reading(s) #9.2 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis Meiosis From Wikipedia, the free encyclopedia In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. The word "meiosis" comes from the Greek meioun, meaning "to make smaller," since it results in a reduction in chromosome number. Meiosis is essential for sexual reproduction. It therefore occurs in most eukaryotes, including single-celled organisms. A few eukaryotes, notably the Bdelloid rotifers, have lost the ability to carry out meiosis and acquired the ability to reproduce by parthenogenesis. Meiosis does not occur in archaea or prokaryotes, which reproduce by asexual cell division processes. During meiosis, the genome of a diploid germ cell, which is composed of long segments of DNA called chromosomes, undergoes DNA replication followed by two rounds of division, resulting in haploid cells called gametes. Each gamete contains one complete set of chromosomes, or half of the genetic content of the original cell. These resultant haploid cells can fuse with other haploid cells of the opposite gender or mating type during fertilization to create a new diploid cell, or zygote. Thus, the division mechanism of meiosis is a reciprocal process to the joining of two genomes that occurs at fertilization. Because the chromosomes of each parent undergo genetic recombination during meiosis, each gamete, and thus each zygote, will have a unique genetic blueprint encoded in its DNA. In other words, meiosis is the process that produces genetic variation. Biochemically, meiosis uses some of the same mechanisms employed during mitosis to accomplish the redistribution of chromosomes. There are several features unique to meiosis, most importantly the pairing and recombination between homologous chromosomes, which enable them to separate from each other. Contents 1 History 2 Occurrence of meiosis in eukaryotic life cycles 3 Process 3.1 Meiosis I 3.1.1 Prophase I 3.1.2 Metaphase I 3.1.3 Anaphase I 3.1.4 Telophase I 4 =Meiosis II 5 Significance of meiosis 6 Nondisjunction 7 Meiosis in humans 8 External links 1 of 6 23/11/06 15:14 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis 9 See also History Meiosis was discovered and described for the first time in sea urchin eggs in 1876, by noted German biologist Oscar Hertwig (1849-1922). It was described again in 1883, at the level of chromosomes, by Belgian zoologist Edouard Van Beneden (1846-1910), in Ascaris worms' eggs. The significance of meiosis for reproduction and inheritance, however, was described only in 1890 by German biologist August Weismann (1834-1914), who noted that two cell divisions were necessary to transform one diploid cell into four haploid cells if the number of chromosomes had to be maintained. In 1911 the American geneticist Thomas Hunt Morgan (1866-1945) observed crossover in Drosophila melanogaster meiosis and provided the first true genetic interpretation of meiosis. Occurrence of meiosis in eukaryotic life cycles Meiosis occurs in all eukaryotic life cycles involving sexual reproduction, comprising of the constant cyclical process of meiosis and fertilization. This takes place alongside normal mitotic cell division. In multicellular organisms, there is an intermediary step between the diploid and haploid transition where the organism grows. The organism will then produce the germ cells that continue in the life cycle. The rest of the cells, called somatic cells, function within the organism and will die with it. The organism phase of the life cycle can occur between the haploid to diploid transition or the diploid to haploid transition. Some species are diploid, grown from a diploid cell called the zygote. Others are haploid instead, spawned by the proliferation and differentiation of a single haploid cell called the gamete. Humans, for example, are diploid creatures. Human stem cells undergo meiosis to create haploid gametes, which are sperm cells for males or ova for females. These gametes then fertilize in the uterus of the female, producing a diploid zygote. The zygote undergoes progressive stages of mitosis and differentiation to create an embryo, the early stage of human life. Gametic life cycle. Zygotic life cycle. There are three types of life cycles that utilise sexual reproduction, differentiated by the location of the organisms stage. In the gametic life cycle, of which humans are a part, the living organism is diploid in nature. Here, we will generalize the example of human reproduction stated previously. Sporic life cycle. The organism's diploid germ-line stem cells undergo meiosis to create haploid gametes, which fertilize to form the zygote. The diploid zygote undergoes repeated cellular division by mitosis to grow into the organism. Mitosis is a related process to meiosis that creates two cells that are genetically identical to the parent cell. The general principle is that mitosis creates somatic cells and meiosis creates germ cells. In the zygotic life cycle, the living organism is haploid. Two organisms of opposing gender contribute their haploid germ cells to form a diploid zygote. The zygote undergoes meiosis immediately, creating four haploid cells. These cells undergo mitosis to create the organism. Many fungi and many protozoa are members of the zygotic life cycle. 2 of 6 23/11/06 15:14 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis Finally, in the sporic life cycle, the living organism alternates between haploid and diploid states. Consequently, this cycle is also known as the alternation of generations. The diploid organism's germ-line cells undergo meiosis to produce gametes. The gametes proliferate by mitosis, growing into a haploid organism. The haploid organism's germ cells then combine with another haploid organism's cells, creating the zygote. The zygote undergoes repeated mitosis and differentiation to become the diploid organism again. The sporic life cycle can be considered a fusion of the gametic and zygotic life cycles, and indeed its diagram supports this conclusion. Process Because meiosis is a "one-way" process, it cannot be said to engage in a cell cycle as mitosis does. However, the preparatory steps that lead up to meiosis are identical in pattern and name to the interphase of the mitotic cell cycle. Interphase is divided into three phases: Gap 1 (G1 ) phase: Characterized by increase in cell size due to accelerated manufacture of organelles, proteins, and other cellular matter. Synthesis (S) phase: The genetic material is replicated: each of its single stranded components replicates into a double stranded structure. The cell thereby transforms from diploid to tetraploid. Gap 2 (G2 ) phase: The cell continues to grow. Interphase is immediately followed by meiosis I and meiosis II. Meiosis I consists of segregating the homologous chromosomes from each other, then dividing the tetraploid cell into two diploid cells each containing one of the segregates. Meiosis II consists of decoupling each chromosome's sister strands (chromatids), segregating the DNA into two sets of strands (each set containing one of each homolog), and dividing both diploid cells to produce four haploid cells. Meiosis I and II are both divided into prophase, metaphase, anaphase, and telophase subphases, similar in purpose to their analogous subphases in the mitotic cell cycle. Therefore, meiosis encompasses the interphase (G1 , S, G2 ), meiosis I (prophase I, metaphase I, anaphase I, telophase I), and meiosis II (prophase II, metaphase II, anaphase II, telophase II). Meiosis I Prophase I In the prophase stage, the cell's genetic material, which is normally in a loosely arranged pile known as chromatin, condenses into visible threadlike structures. Along the thread, centromeres are visible as small beads of tightly coiled chromatin. The first stage of Prophase I is the leptotene stage, during which individual chromosomes begin to condense into long strands within the nucleus. The zygotene stage then occurs as the chromosomes approximately line up with each other into homologous chromosomes. The combined homologous chromosomes are said to be bivalent. They may also be referred to as a tetrad, a reference to the four sister chromatids. During this stage, one percent of DNA that wasn't replicated during S phase is replicated. The significance of this cleanup act is unclear. The pachytene stage heralds crossing over. Nonsister chromatids of homologous chromosomes randomly exchange segments of genetic information. Because the chromosomes cannot be distinguished in the synaptonemal complex, the actual act of crossing over is not perceivable through the microscope. 3 of 6 23/11/06 15:14 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis During the diplotene stage, the synaptonemal complex degrades. Homologous chromosomes fall apart and begin to repel each other. The chromosomes themselves uncoil a bit, allowing some transcription of DNA. They are held together by virtue of recombination nodules, betraying the sites of previous crossing over, the chiasmata. Chromosomes recondense during the diakinesis stage. Sites of crossing over entangle together, effectively overlapping, making chiasmata clearly visible. In general, every chromosome will have crossed over at least once. This means that the pairs of homologous chromosomes are so tightly packed they exchange genetic material. The nucleoli disappears and the nuclear membrane disintegrates into vesicles. During these stages, centrioles are migrating to the two poles of the cell. These centrioles, which were duplicated during interphase, function as microtubule coordinating centers. Centrioles sprout microtubules, essentially cellular ropes and poles, during crossing over. They invade the nuclear membrane after it disintegrates, attaching to the chromosomes at the kinetochore. The kinetochore functions as a motor, pulling the chromosome along the attached microtubule toward the originating centriole, like a train on a track. There are two kinetochores on each tetrad, one for each centrosome. Prophase I is the longest phase in meiosis. Microtubules that attach to the kinetochores are known as kinetochore microtubules. Other microtubules will interact with microtubules from the opposite centriole. These are called nonkinetochore microtubules. Metaphase I As kinetochore microtubules from both centrioles attach to their respective kinetochores, the homologous chromosomes align equidistant above and below an imaginary equatorial plane, due to continuous counterbalancing forces exerted by the two kinetochores of the bivalent. Because of independent assortment, the orientation of the bivalent along the plane is random. Maternal or paternal homologues may point to either pole. Anaphase I Kinetochore microtubules shorten, severing the recombination nodules and pulling homologous chromosomes apart. Since each chromosome only has one kinetochore, whole chromosomes are pulled toward opposing poles, forming two haploid sets. Each chromosome still contains a pair of sister chromatids. Nonkinetochore microtubules lengthen, pushing the centrioles further apart. The cell elongates in preparation for division down the middle. Also Homologous pairs line up together at the metaphase plate. Telophase I The first meiotic division effectively ends when the centromeres arrive at the poles. Each daughter cell now has half the number of chromosomes but each chromosome consists of a pair of chromatids. The microtubules that make up the spindle network disappear, and a new nuclear membrane surrounds each haploid set. The chromosomes uncoil back into chromatin. Cytokinesis, the pinching of the cell membrane in animal cells or the formation of the cell wall in plant cells, occurs, completing the creation of two daughter cells. Cells enter a period of rest known as interkinesis or interphase II. No DNA replication occurs during this stage. Note that many plants skip telophase I and interphase II, going immediately into prophase II. =Meiosis II 4 of 6 23/11/06 15:14 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis Prophase II takes an inversely proportional time compared to telophase I. In this prophase we see the disappearance of the nucleoli and the nuclear envelope again as well as the shortening and thickening of the chromatids. Centrioles move to the polar regions and are arranged by spindle fibres. The new equatorial plane is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plane. In metaphase II, the centromeres contain three kinetochores, organizing fibers from the centrosomes on each side. This is followed by anaphase II, where the centromeres are cleaved, allowing the kinetochores to pull the sister chromatids apart. The sister chromatids by convention are now called sister chromosomes, and they are pulled toward opposing poles. The process ends with telophase II, which is similar to telophase I, marked by uncoiling, lengthening, and disappearance of the chromosomes occur as the disappearance of the microtubules. Nuclear envelopes reform; cleavage or cell wall formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes. Meiosis is complete. Significance of meiosis Meiosis facilitates stable sexual reproduction. Without the halving of ploidy, or chromosome count, fertilization would result in zygotes that have twice the number of chromosomes than the zygotes from the previous generation. Successive generations would have an exponential increase in chromosome count, resulting in an unwieldy genome that would cripple the reproductive fitness of the species. Polyploidy, the state of having three or more sets of chromosomes, also results in developmental abnormalities or lethality. Most importantly, however, meiosis produces genetic variety in gametes that propagate to offspring. Recombination and independent assortment allow for a greater diversity of genotypes in the population. As a system of creating diversity, meiosis allows a species to maintain stability under environmental changes. Nondisjunction The normal separation of chromosomes in Meiosis I or sister chromatids in meiosis II is termed disjunction. When the separation is not normal, it is called nondisjunction. This results in the production of gametes which have either more or less of the usual amount of genetic material, and is a common mechanism for trisomy or monosomy. Nondisjunction can occur in the meiosis I or meiosis II phases of cellular reproduction, or during mitosis. This is a cause of several medical conditions in humans, including: Down Syndrome - trisomy of chromosome 21 Patau Syndrome - trisomy of chromosome 13 Edward Syndrome - trisomy of chromosome 18 Klinefelter Syndrome - an extra X chromosome in males Turner Syndrome - only one X chromosome present in females XYY Syndrome - an extra Y chromosome in males Triple X Syndrome - an extra X chromosome in females Meiosis in humans In females, meiosis occurs in precursor cells known as oogonia that divide twice into oocytes. These stem cells stop at the diplotene stage of meiosis I and lay dormant within a protective shell of somatic cells called 5 of 6 23/11/06 15:14 Meiosis - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Meiosis the follicle. Follicles begin growth at a steady pace in a process known as folliculogenesis, and a small number enter the menstrual cycle. Menstruated oocytes continue meiosis I and arrest at meiosis II until fertilization. The process of meiosis in females is called oogenesis, and differs from the typical meiosis in that it features a long period of meiotic arrest known as the Dictyate stage and lacks the assistance of centrosomes. In males, meiosis occurs in precursor cells known as spermatogonia that divide twice to become sperm. These cells continuously divide without arrest in the seminiferous tubules of the testicles. Sperm is produced at a steady pace. The process of meiosis in males is called spermatogenesis. External links Comparison of Meiosis and Mitosis (1) (http://www.maxanim.com/genetics/Comprarison%20of%20Meiosis%20and%20Mitosis/Comprarison%20of%20Mei Stages of Meiosis (2) (http://www.maxanim.com/genetics/Stages%20of%20Meiosis/Stages%20of%20Meiosis.htm) (Flash Animations) See also Mitosis Ploidy Spermatogenesis Oogenesis Retrieved from "http://en.wikipedia.org/wiki/Meiosis" Category: Cell biology This page was last modified 06:22, 21 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 6 of 6 23/11/06 15:14 Reading(s) #10 Reading(s) #10.1 Terminator (genetics) - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Terminator_(genetics) Terminator (genetics) From Wikipedia, the free encyclopedia In genetics, a terminator, or transcription terminator is a section of genetic sequence that marks the end of gene or operon on genomic DNA for transcription. In prokaryotes, two classes of transcription terminators are known: 1. Intrinsic transcription terminators where a hairpin structure forms within the nascent transcript that disrupts the mRNA-DNA-RNA polymerase ternary complex. 2. Rho-dependent transcription terminators that require Rho factor, an RNA helicase protein complex to disrupt the nascent mRNA-DNA-RNA polymerase ternary complex. In eukaryotes, terminators are recognized by protein factors that co-transcriptionally cleave the nascent RNA at a polyadenylation signal, halting further elongation of the transcript by RNA polymerase. The subsequent addition of the poly-A tail at this site stabilizes the mRNA and allows it to be exported outside the nucleus. Terminator sequences are distinct from termination codons that occur in the mRNA and are the stopping signal for translation, which may also be called nonsense codons. A transcription terminator must also be distinguished from the dideoxynucleotides added to a dye terminator sequencing. Retrieved from "http://en.wikipedia.org/wiki/Terminator_%28genetics%29" Categories: Genetics stubs | Genetics This page was last modified 22:37, 4 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 1 of 1 23/11/06 15:14 Reading(s) #10.2 Terminator Technology - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Terminator_Technology Terminator Technology From Wikipedia, the free encyclopedia Terminator Technology is the colloquial name given to proposed methods for restricting the use of genetically modified plants by causing second generation seeds to be sterile. The technology was under development by the U.S. Department of Agriculture and Delta and Pine Land Company in the 1990s and is not yet commercially available. Because some stakeholders expressed concerns that this technology might lead to dependence for poor smallholder farmers, Monsanto, an agricultural products company and the world's biggest seed supplier, pledged (http://www.guardian.co.uk/international/story/0,3604,260202,00.html) not to commercialize the technology even if and when it becomes commercially available. The technology was discussed during the 8th Conference of the Parties to the UN's Convention on Biological Diversity in Curitiba, Brazil, March 20-31, 2006. Terminator Technology is one form of Genetic Use Restriction Technologies (GURT). There are conceptually two types of GURT. 1. V-GURT This type of GURT produces sterile seeds meaning that a farmer that had purchased seeds containing v-GURT technology could not save the seed from this crop for future planting. This would not have an immediate impact on the large number of farmers who use hybrid seeds, as they do not produce their own planting seeds, and instead buy specialized hybrid seeds from seed production companies. The technology is restricted at the plant variety level - hence the term V-GURT. Manufacturers of genetically enhanced crops would use this technology to protect their products from unauthorised use. 2. T-GURT. A second type of GURT modifies a crop in such a way that the genetic enhancement engineered into the crop does not function until the crop plant is treated with a chemical that is sold by the biotechnology company. Farmers can save seeds for use each year. However, they do not get to use the enhanced trait in the crop unless they purchase the activator compound. The technology is restricted at the trait level - hence the term T-GURT. Possible Advantages of GURT technology 1. An Incentive to the Development of New Plant Varieties Where effective intellectual property protection systems don't exist or are not enforced, GURTs could be an alternative to stimulate plant developing activities by biotech firms. 2. Improved Farm Management Non-viable seed produced on V-GURT plants will reduce the propagation of volunteer plants. Volunteer plants can become an economic problem for larger-scale mechanized farming systems that incorporate crop rotation. 3. Improved grain quality Under warm, wet harvest conditions non V-GURT grain can sprout, which lowers the quality of grain produced. It is speculated that this problem would not occur with the use of V-GURT grain varieties. 1 of 2 23/11/06 15:15 Terminator Technology - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Terminator_Technology 4. Biosafety Use of V-GURT technology could prevent escape of transgenes into wild relatives and prevent any impact on biodiversity. Crops modified to produce non-food products could be armed with GURT technology to prevent accidental transmission of these traits into crops destined for foods. Possible Disadvantages of GURT Technology 1. Transmission of the "Terminator" trait to wild plants, or cultivated plants whose seeds are saved There is a concern that V-GURT plants could cross-pollinate with non-genetically modified plants, either in the wild or on the fields of farmers who do not adopt the technology. Though the V-GURT plants are supposed to produce sterile seeds, there is concern that this trait will not be expressed in the first generation of a small percentage of these plants, but be expressed in later generations. This does not seem to be much of a problem in the wild, as a sterile plant would naturally be selected out of a population within one generation of trait expression. This is however a problem in some farming systems, especially for indigenous groups who save seed rather than purchase it from developers. The loss of the ability for such farmers to save seed may lead to decreased agroecological biodiversity on their farms and decreased yields of affected crops. 2. Safety of Food produced from GURT crops As with all Genetically Modified crops the food safety of GURT technology would need to be assessed when and if a commercial release of a GURT containing crop was proposed. 3. The inequitable distribution of means; the targeting of vulnerable classes In addition to potential biological and ecological harms, there is both an economic and normative concern that small farmers, indigenous peoples, and entire rural communities could be made dependent on agro-industry corporations for seed. 4. A presumption of entitlement As with many other technologies, there is debate as to the role and responsibility implicit in the normative assumptions involved in producing GURTs. The issue is distinct from the conflict surrounding the production of GM foods generally, in that GURT products are specifically designed to affect future generations and potentially have a distinct impact on human and ecological health and livelihoods. Thus, some believe that in making decisions regarding such products, considerations should extend beyond what is legally permissible. Retrieved from "http://en.wikipedia.org/wiki/Terminator_Technology" This page was last modified 22:03, 2 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 2 of 2 23/11/06 15:15 Reading(s) #10.3 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism Genetically modified organism From Wikipedia, the free encyclopedia A genetically modified organism (GMO) is an organism whose genetic material has been altered using techniques in genetics generally known as recombinant DNA technology. Recombinant DNA technology is the ability to combine DNA molecules from different sources into one molecule in a test tube. Thus, the abilities or the phenotype of the organism, or the proteins it produces, can be altered through the modification of its genes. The term generally does not cover organisms whose genetic makeup has been altered by conventional cross breeding or by "mutagenesis" breeding, as these methods predate the discovery of the recombinant DNA techniques. Technically speaking, however, such techniques are by definition genetic modification. A tobacco plant which has Examples of GMOs are diverse, and include transgenic experimental animals been genetically such as mice, several fish species, transgenic plants, or various microscopic engineered to express a organisms altered for the purposes of genetic research or for the production of gene taken from fireflies. pharmaceuticals. The term "genetically modified organism" does not necessarily imply, but does include, transgenic substitution of genes from another species, and research is actively being conducted in this field. For example, genes for fluorescent proteins can be co-expressed with complex proteins in cultured cells to facilitate study by biologists, and modified organisms are used in researching the mechanisms of cancer and other diseases. Contents 1 2 3 4 5 6 7 8 9 History of GMO Methods of genetic modification Genetic modification of plants Genetic modification of animals Controversy Transgenics featured in fiction References See also External links History of GMO The first GMO was created in 1973 by Stanley N. Cohen and Herbert Boyer, demonstrating the creation of a functional organism that combined and replicated genetic information from different species. [1] (http://www.genomenewsnetwork.org/resources/timeline/1973_Boyer.php) . In mid-1974, very soon after the first GMO was created, scientists called for and observed a voluntary moratorium on certain recombinant DNA experiments. One goal of the moratorium was to provide time for a conference that would evaluate the state of the new technology and the risks, if any, associated with it. That conference concluded that recombinant DNA research should proceed but under strict guidelines. Such guidelines were subsequently promulgated by the National Institutes of Health in the United States and by comparable bodies in other 1 of 6 23/11/06 15:15 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism countries. These guidelines form the basis upon which GMOs are regulated to this day. [2] (http://nobelprize.org/chemistry/articles/berg/) The first transgenic animals were mice created by Rudolf Jaenisch in 1974. Jaenish successfully managed to insert foreign DNA into the early-stage mouse embryos; the resulting mice carried the modified gene in all their tissues. Subsequent experiments, injecting leukemia genes to early mouse embryos using a retrovirus vector, proved the genes integrated not only to the mice themselves, but also to their progeny. Methods of genetic modification Genetic modification involves genetic engineering, also known as gene splicing, a technique to splice together DNA fragments from more than one organism and thus preparing a "recombinant" DNA molecule in a test tube, producing a single piece of genetic material containing the original information from multiple fragments which can then be inserted into another organism. This is achieved by cutting up DNA molecules with restriction enzymes and splicing these fragments together using DNA ligase. A transgenic organism that contains such DNA sequences from a foreign organism integrated into its own genome, the term "transgenic" literally means across gene. A mouse or fish engineered to express the green fluorescence protein, for example, would be considered a transgenic organism, since the gene coding for the protein originated from a species of jellyfish. With current technology, transgenic organisms can be produced with only a very small proportion of extraneous DNA. For example, the genome of most mammals contains three billion basepairs of DNA, while it becomes relatively difficult to insert more than 10,000 to 20,000 basepairs of foreign DNA. More sophisticated techniques using yeast artificial chromosomes and bacterial artificial chromosomes allow insertions of up to 320,000 basepairs [3] The double-helix structure of DNA allows modification of plasmids to take place. (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11884478&quer - approximately 0.01% of the total genome. In concept, multiple rounds of transgenesis or interbreeding of transgenics could lead to organisms with a higher proportion of foreign DNA, but cost and time considerations prevent this. In order to introduce new DNA into the receiving host, vectors are used. Vectors range from small circular pieces of DNA such as plasmids, to various viruses that can carry and transmit genetic information. Three processes are known by which the genetic composition of bacteria can be altered. Transformation is a process by which some bacteria are naturally capable of taking up DNA to acquire new genetic traits. This phenomenon was discovered in cows by Frederick Griffith in 1928, although the fact that it was specifically DNA molecules that carried the genetic information was not proven until 1944. Bacteria that are competent to undergo transformation are frequently used in molecular biology. The foreign DNA uptake is facilitated by the presence of certain cations, such as Ca2+, or by the use of electric current (electroporation). Transformation does not normally integrate new DNA into the bacterial chromosome. Instead, it remains on a plasmid. In conjugation, DNA is transferred from one bacterium to another via a temporary connecting tube of protein called a pilus (a process analogous to but biologically distinct from mating). A plasmid is transferred through the pilus. Conjugation is not widely used for the artificial genetic modification of bacteria, but 2 of 6 23/11/06 15:15 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism happens often in nature. Transduction refers to the introduction of new DNA into a bacterial cell by a bacteriophage, a virus that infects bacteria. In order to gain knowledge about a particular gene's function, researchers often use knock out organisms. These organisms have a specific gene that has been functionally destroyed or "knocked out." They are used extensively in disease research with model organisms. For example, when investigating the cause of cystic fibrosis, researchers identified the CFTR gene as a likely candidate for the disease, found the mouse equivalent, bred a mouse with this gene "knocked out", and noted that the knockout mouse also had cystic fibrosis. Genetic modification of plants Genetic modification of animals Like bacteria and plants, animals can be genetically modified by viral infection. However, the genetic modification occurs only in those cells that become infected, and in most cases these cells are eventually eliminated by the immune system. In some cases it is possible to use the gene-transferring ability of viruses for gene therapy, i.e. to correct diseases caused by a defective gene by supplying a normal copy of the gene. Permanent genetic modification of entire animals can be accomplished in mice. The process begins by first genetically modifying a mouse embryonic stem cell. This is normally done by physically introducing into the cell a plasmid that can integrate into the genome by a process known as transfection [4] (http://www.yotor.com/wiki/en/tr/Transfection.htm) . During transfection the DNA integrates into the animal genome via non-homologous recombination. This altered cell is implanted into a blastocyst (an early embryo), which is then implanted into the uterus of a female mouse. A pup born from this blastocyst will be a chimera containing some cells derived from the unmodified cells of the blastocyst and some derived from the modified stem cell. By selecting mice whose germ cells (sperm- or egg-producing cells) developed from the modified cell and interbreeding them, pups that contain the genetic modification in all of their cells will be born. Baylor College of Medicine currently has one of the largest transgenic mice facilities in the country. There has also been the genetically manipulated bull Herman with 55 offspring. A human gene was built into his genetic code while in an early embryonic stage in 1990. As a result, milk from his female descendants contained the human protein lactoferrine, which can be used as medicine, but it was present at such low levels that it was not profitable to extract them. Insects can be genetically modified by injecting them with artificial transposons and a source of the enzyme transposase. The transposon, which can include new genes, is then integrated into the genome. Such insertions are unstable and can 'jump-out' in the presence of transposase. Transgenic fish are often created by microinjection. First generation is mosaic but several lines have been produced with the transgene incorporated into the germ line and transgenic fish can then be produced "naturally" by crossing male and female gametes. Although many types of transgenic fish exist (e.g. for increased cold tolerance, antibiotic production, ornamental Glofish etc), the main focus had been on so-called growth hormone transgenic fish, mainly salmonids, tilapias and carps. These fish have an over-production of growth hormone which results in increased growth rate from a few percent up to 30-40 times that of wild-types. In some species, final size is increased as well as growth rate providing an incentive for commercial breeders to farm such fish. However, ecological concerns over potential negative effects of transgenic fish in nature largely prevent the commencement of commercial production. A large and important portion of the research on transgenic fish today is therefore focused on environmental 3 of 6 23/11/06 15:15 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism risk-assessment of GH-transgenic fish. Problems encountered and advances within this field are summarized in Devlin et al (2006). Controversy See also Genetically modified food and Transgenic plants Genetic modification (GM) is not the subject of controversy in its own right [5] (http://www.csa.com/hottopics/gmfood/overview.php) . Some see the science itself as intolerable meddling with "natural" order, despite many known examples of natural genetic crossings occurring throughout history (see for example horizontal gene transfer). While some would like to see it banned, others push simply for required labeling of genetically modified food. Other controversies include the definition of patent and property pertaining to products of genetic engineering and the possibility of unforeseen global side effects as a result of modified organisms proliferating. The basic ethical issues involved in genetic research are discussed in the article on genetic engineering. In 1986, field tests of a bacterium genetically engineered to protect plants from frost damage at a small biotechnology company called Advanced Genetic Sciences of Oakland, California, were repeatedly delayed by opponents of biotechnology. Also in 1986, a proposed field test of a microbe genetically engineered for a pest resistance protein by Monsanto was dropped.[6] (http://homepages.uel.ac.uk/J.Mottley/Newchapt.html) In 2004, Mendocino County, California became the first county in the United States to ban the production of GMOs. The measure passed with a 57% majority. In 2005, a standing committee of the government of Prince Edward Island in Canada began work to assess a proposal to ban the production of GMOs in the province. This is a largely symbolic and empty gesture as PEI has already banned GM potatoes, which account for most of its crop. In California, Trinity and Marin counties have also imposed bans on GM crops, while ordinances to do so were unsuccessful in Butte, San Luis Obispo, Humboldt, and Sonoma counties. Supervisors in the agriculturally-rich counties of Fresno, Kern, Kings, Solano, Sutter, and Tulare have passed resolutions supporting the practice [7] (http://www.santacruzsentinel.com/archive/2005/June/15/local/stories/07local.htm) . Currently, there is little international consensus regarding the acceptability and effective role of modified "complete" organisms such as plants or animals. A great deal of the modern research that is illuminating complex biochemical processes and disease mechanisms makes vast use of genetic engineering. The practice of genetic modification as a scientific technique is not restricted in the United States. Individual genetically modified crops (such as soybeans) are subject to intense study before being brought to market and are common in the United States, but estimates of their market saturation vary widely. Most countries in Europe, Japan, Mexico (among others) have taken the opposite position, stating that genetic modification has not been proven safe, and therefore that they will not accept genetically modified food from the United States or any other country. This issue has been brought before the World Trade Organization, which determined that not allowing modified food into the country creates an unnecessary obstacle to international trade. Consequently, genetic modification within agriculture is an issue of some strong debate in the United States, the European Union, and some other countries. Some critics have raised the concern that conventionally bred crop plants can be cross-pollinated (bred) from the pollen of modified plants. Pollen can be dispersed over large areas by wind, animals, and insects. Recent research with creeping bentgrass has lent support to the concern when modified genes were found in normal grass up to 21 km (13 miles) away from the source, and also within close relatives of the same genus 4 of 6 23/11/06 15:15 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism (Agrostis) [8] (http://www.pnas.org/cgi/content/abstract/101/40/14533?ijkey=e52c2f60e681a753eab3d267158057b81ffc6b13&keytyp . GM proponents point out that outcrossing, as this process is known as, is not new. The same thing happens with any new open-pollinated crop variety—newly introduced traits can potentially cross out into neighbouring crop plants of the same species and, in some cases, to closely related wild relatives. Defenders of GM technology point out that each GM crop is assessed on a case by case basis to determine if there is any risk associated with the outcrossing of the GM trait into wild plant populations. The fact that a GM plant may outcross with a related wild relative is not, in itself, a risk unless such an occurrence has consequences. If, for example, a herbicide resistance trait was to cross into a wild relative of a crop plant it can be predicted that this would not have any consequences except in areas where herbicides are sprayed, such as a farm. In such a setting the farmer can manage this risk by rotating herbicides. If patented genes are outcrossed, even accidentally, to other commercial fields and a person deliberately selects the outcrossed plants for subsequent planting then the patent holder has the right to control the use of those crops. This was supported in Canadian law in the case of Monsanto Canada Inc. v. Schmeiser. The documentary The Future of Food covers the GMO and Monsanto controversy in more depth. An often cited controversy is a hypothetical Technology Protection technology (dubbed terminator by non-governmental organization). This yet-to-be-commercialised technology would allow the production of first generation crops that would not generate seeds in the second generation because the plants yield sterile seeds. The patent for this so-called "terminator" gene technology is owned by Delta and Pine Land and the United States Department of Agriculture. Delta and Pine Land was bought by Monsanto in August 2006. In addition to the commercial protection of proprietary technology in selfpollinating crops such as soybean (a generally contentious issue) another purpose of the terminator gene is to prevent the escape of genetically modified traits from crosspollinating crops into wild-type species by sterilizing any resultant hybrids. The terminator gene technology created a backlash amongst those who felt the technology would prevent re-use of seed by farmers growing such terminator varieties in the developing world and was ostensibly a means to exercise patent claims. Use of the terminator technology would also prevent "volunteers", or crops that grow from unharvested seed, a major concern that arose during the Starlink debacle. For more information on this topic see the [Greenpeace][9] (http://weblog.greenpeace.org/ge/) GE website. Transgenics featured in fiction Genetically modified characters, whether as heroes, villains, or backdrop, feature prominently in many works of fiction, in particular science fiction and cyberpunk, where it is used as a plot device to explain differences in a character or setting, such as explaining increased longevity or eradication of disease in a fictional civilization. In the Spider-Man movie, Peter Parker was bitten by a super-spider, enhanced with the genes of many different spiders. The abilities of all these spiders were then transferred from the super-spider, into Peter, turning him into Spider-Man. The videogame character Shadow the Hedgehog was originally a science experiment who was fused with the DNA of Black Doom, causing him to have the genes of aliens as well as hedgehogs. This however, was not revealed until the game Shadow the Hedgehog. Dark Angel deals with transgenics escaped from a secret government facility. The main character Max, a human / cat transgenic engineered to be a supersoldier in future warefare, tries to lead a normal life while searching for others of her kind. 5 of 6 23/11/06 15:15 Genetically modified organism - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Genetically_modified_organism In the Maximum Ride books by James Patterson, the main characters are human/bird transgenics. In Red Dwarf, mankind turns to GELFs, Genetically Engineered LifeForms, after the robot revolution leaves them with nothing. References Anderson, K. and Lee Ann Jackson. 2005. Some Implications of GM Food Technology Policies for Sub-Saharan Africa. Journal of African Economies 14(3):385-410; doi:10.1093/jae/eji013 Heong, KL, YH Chen, DE Johnson, GC Jahn, M Hossain, RS Hamilton. 2005. Debate Over a GM Rice Trial in China. Letters. Science, Vol 310, Issue 5746, 231-233 , 14 October 2005. Huang, J., Ruifa Hu, Scott Rozelle, Carl Pray. 2005. Insect-Resistant GM Rice in Farmers' Fields: Assessing Productivity and Health Effects in China. Science (29 April 2005) Vol. 308. no. 5722, pp. 688 – 690. DOI: 10.1126/science.1108972 See also Genetically modified food Fish Farming External links International Conference on "GM Crops and Foods" (20/21 November in Frankfurt/Germany) (http://www.akademie-fresenius.de/1824) Everything you wanted to know about GM organisms (http://www.newscientist.com/channel/life/gm-food) — Provided by New Scientist. Genetically Modified Organisms (http://www.organicfooddirectory.com.au/gmo.php) - Information about GMOS and GE Eppendorf Biochip Systems (http://www.eppendorf-biochips.com) Detection method for GMO in food and feed by using GMO-microarray Nature 2.0 beta | Legislation, Politics, Science and Spin Behind Genetically Modified Foods (http://thegreenreport.com/nature2.0) Food Security and Ag-Biotech News (http://www.merid.org/fs-agbiotech/) — for balanced news Devlin RH, Sundstrom LF, Muir WM. 2006. Interface of biotechnology and ecology for environmental risk assessments of transgenic fish. Trends in Biotechnology 24:89-97 (http://dx.doi.org/10.1016/j.tibtech.2005.12.008) - A scientific article on the advances and problems in making reliable risk-assessment of transgenic fish. Bernard Stiegler, "Take Care" (http://www.arsindustrialis.org/Members/bstiegler/prendresoin-en) — A philosophical approach to the question of GMOs and their relation to human agricultural history. Retrieved from "http://en.wikipedia.org/wiki/Genetically_modified_organism" Categories: Articles lacking sources | Genetically modified organisms | Molecular biology This page was last modified 06:48, 20 November 2006. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc. 6 of 6 23/11/06 15:15 Reading(s) #11 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... University Libraries-University at Buffalo-State Univ. of NY Expanded Academic ASAP The Ecologist, Sept-Oct 1998 v28 n5 p276(4) Terminator Technology: the threat to world food security. Ricarda A. Steinbrecher; Pat Roy Mooney. Author's Abstract: COPYRIGHT 1998 The Ecologist (UK) Monsanto's latest flagship technology makes a nonsense of its claim that it seeks to feed the worlds hungry. On the contrary, it threatens to undermine the very basis of traditional agriculture - that of saying seeds from year to year. What's more, this "gene cocktail" will increase the risk that new toxins and allergens will make their way into the food chain. Full Text: COPYRIGHT 1998 The Ecologist (UK) In 1860, fully five years before Abbe Gregor Mendel published his obscure tome on the genetics of peas, launching so-called "modern" plant breeding, a certain Major Hallett, F.L.S., of Brighton was warning farmers and fellow seedsmen that any abuse of his "pedigree" trademark for cereals would be "severely dealt with".[1] But his seeds were not patentable and there was little he could do to keep farmers from buying his wheat varieties, sowing them, selecting the best seed for the next season, and breeding their own varieties uniquely adapted to local soils, slopes, and weather. It was only in 1908 that George Shull came up with what Major Hallett really wanted - a biological weapon to keep farmers from saving and developing their own seeds. Called "hybridization", a wonderfully euphemistic term that led farmers to think that crossing two distant plant relatives could create a "hybrid vigour" that so improved yield as to make the resulting seed sterility - meaning it could not be replanted - financially worthwhile.[2] Today, almost every ear of corn grown from California to Kazakhstan is a hybrid controlled by any one of a handful of very large seed companies. Exactly 90 years after Shull's revelation, one of the biggest and most powerful of those companies, Monsanto, is fighting for control of the most important seed monopoly technology since the hybrid. But unlike 1860, this piece of life control can be patented. On March 3rd, the US Department of Agriculture (USDA) and a little-known cotton-seed enterprise called Delta and Pine Land Company, acquired US patent 5,723,765 - or the Technology Protection System (TPS). Within days, the rest of the world knew TPS as Terminator Technology. Its declared goal is to promulgate plants that will produce self-terminating off-spring - suicide seeds. Terminator Technology epitomizes what the genetic engineering of food crops is all about and gives an insight into the driving forces behind the corporate campaign to control and own life. The Terminator rides to the rescue of long-suffering multinationals who have been unable to hold farmers back from their 12,000 year tradition of saving and breeding seeds. Farmers buy the seed once and do their own work thereafter. Patents and Pinkerton detectives have been employed to stop farmers from doing so. The Terminator though provides a built-in biological "patent", enforced by engineered genes. Small farming communities of the Third World especially, rely upon their own plant breeding since neither corporate nor public breeders show much interest or aptitude in breeding for their often difficult environments. Old-fashioned hybrids and the Terminator Technology with its terminated seeds force farmers back to the market every season. Terminator also scuttles community conservation of agricultural biodiversity. There's nothing to conserve. It is the "neutron bomb" of agriculture. 1 of 6 23/11/06 15:16 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... Hybrid seeds Following the rediscovery of Mendel's Laws in 1900, money-minded plant breeders pursued strategies that would force farmers back to the marketplace every season to spend their hard-earned money on seeds. Although the concept of hybrids evolved with George Shull in 1908, the first hybrid maize was not commercialized until 1924 by Henry A. Wallace. Two years later, Wallace formed Pioneer Hi-Bred the world's largest seed company and still largely controlled by the founding family. Wallace went onto become US Secretary of Agriculture and, finally (in 1941), Vice-President of the United States. Wallace's championship of hybrids made it an immutable, if unscientific, Act of Faith to argue that "hybrid vigour" made maize the "bin-busting" bonanza it is today. More recently, however, respected scientific and economic critics like Jean-Pierre Berlan of France's INRA and Richard C. Lewontin of Harvard, as well as Jack R Kloppenburg Jr. of the University of Wisconsin, have challenged this assumption insisting that conventional maize-breeding programmes would always out-perform hybrids given the same research investment. According to these critics, the only advantage to hybrids lies in their profitability for companies. How hybrids work Hybrid seeds are the first generation (F1) progeny of two distinct and distant parental lines of the same species. The seed will incorporate and express the desired genetic traits of each parent for just one generation. Seeds taken from an F1 hybrid may either be sterile or, more commonly, fail to "breed true", not express the desirable genetic qualities found in F1. Farmers in industrialized agricultural systems rarely attempt to replant a hybrid because of the exacting requirements of machine-harvesting and food-processing for crop uniformity. Resource-poor farmers in countries such as Brazil, on the other hand, will often take F2 (second generation) hybrid seeds as a source of breeding material to be blended with their traditional varieties. In this way, skilled local breeders, mostly women,be they in Brazil, Burundi or Bangladesh, isolate useful genetic characteristics and adapt them to their immediate market. The most commonly hybridized crops are maize, cotton, sunflowers and sorghum. Until recently, small grain cereals such as rice, wheat, barley, oats, and rye and leguminous crops such as soybeans, have defied such commercial hybridization. Now this is changing. Public breeding initiatives led by governments such as China and institutions such as the Rockefeller Foundation and Cornell University have developed commercial rice hybrids. The seed multinationals are hot on their heels. Most recently, giants like Monsanto and Novartis have been waxing poetic over the prospect of Fl hybrid wheat. With more land sown to wheat than any other crop on the planet, a new hybrid monopoly for this crop would be a windfall for seed companies.[3] Terminator Technology: The Terminator as Biological Warfare on Farmers and Food Security The Terminator does more than ensure that farmers can't successfully replant their harvested seed. It is the "platform" upon which companies can load their proprietary genetic traits - patented genes for herbicide-tolerance or insect-resistance - and get the farmers hooked on their seeds and caught in the chemical treadmill. The Terminator is a guarantee that even Brazil's innovative farmers will have to buy access to these traits every year. The target market for the Terminator is explicitly the South's farmers. Beginning with company news releases announcing the patent, Delta and Pine has trumpeted that its Technology Protection System will make it economically safe for seed companies to sell their high-tech varieties in Africa, Asia and Latin America. The company has even estimated that 405 million hectares will be sown with Terminator seeds within a few years. This is a land mass almost equal to South Asia. Although Terminator Technology has only been tested in cotton and tobacco, its designers are convinced that it can be applied to any species. Delta and Pine has specifically suggested that rice and wheat farmers in countries like India, China and Pakistan are a priority market. According to the company, Terminator 2 of 6 23/11/06 15:16 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... Technology's value could run as high as $4.00 per hectare for upmarket garden crops. The patent could be worth a billion dollars.[4] "The centuries old practice of farmer-saved seed is really a gross disadvantage to Third World farmers who inadvertently become locked into obsolete varieties because of their taking the "easy road" and not planting newer, more productive varieties." - Dr. Harry B. Collins, Delta and Pine Land Co, Vice-President for Technology Transfer (June 12, 1998)[5] How the Terminator Technology works The Terminator Technology is the main application of a broadly framed patent for the "control of plant gene expression". The Terminator is basically a genetically engineered suicide mechanism that can be triggered off by a specific outside stimulus. As a result the seeds of the next generation will self-destruct by self-poisoning. The preferred trigger is the antibiotic tetracycline applied to seeds. The main version of the Terminator consists of a set of three novel genes inserted into one plant [see Box 1]; another version divides two or three genes on to two plants, which are later to be cross-pollinated. The end-result is always a dead seed in the following generation. Terminator Technology is the Trojan Horse for the spread of genetically-engineered crops in the South. In the absence of "effective" patent regimes, companies can still market their wares and enforce constant returns for their investments. In the absence of adequate biosafety legislation, countries might be persuaded to accept the Terminator on the assumption that the technology is safe and that transgenic traits can not survive to a second generation, even by cross-pollination. This assumption is ill-founded. As with all genetic engineering, its direct effect and its side-effects are unpredictable and carry all the risks inherent in this technology. The gene-cocktail of the Terminator increases the risks that new toxins and allergens will show up in our food and animal fodder. Most alarming though is the possibility that the Terminator genes themselves could infect the agricultural gene pool of the neighbour's crops and of wild and weedy relatives, placing a time-bomb. Temporary "gene silencing" of the poison gene or failed activation of the Terminator countdown enables such infection [see Box 2]. Between 15 and 20 per cent of the world's food supply is grown by poor farmers who save their seed. These farmers feed at least 1.4 billion people. The Terminator "protects" companies by risking the lives of these people. Since Terminator Technology has absolutely zero agronomic benefit, there is no reason to jeopardize the food security of the poor by gambling with genetic engineering in the field. Whether the Terminator works immediately or later, in either instance it is biological warfare on farmers and food security. The Terminator also portends a hidden dark side. As a Trojan Horse for other transgenic traits, the technology might also be used to switch any trait off or on. At least in theory, the technology points to the possibility that crop diseases could be triggered by seed exports that would not have to "kick in" immediately - or not until activated by specific chemicals or conditions. This form of biological warfare on people's food and economies is becoming a hot topic in military and security circles.(6) Terminator meets the "Monster" Scarcely two months after USDA and Delta & Pine Land announced the receipt of the Terminator patent, Monsanto bought the company. The announcement of the $1.76 billion purchase came on May 11th even as parties to the Convention on Biological Diversity were meeting in Bratislava. The Terminator had already elbowed its way into conference debates when press stories reached delegations. Overnight the US delegation, who had not uttered a word when even the USDA was under attack for its Terminator involvement, came out fighting for Monsanto. With former Clinton White House staffers on Monsanto's lobby payroll and Mickey Cantor, the US Trade Representative 3 of 6 23/11/06 15:16 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... for much of the Uruguay Round, on Monsanto's board, the American government's zeal was less than surprising. [See Ferrara in this issue] Seed technology has moved a long way since 1860 and the proprietary passions of Major Hallett. Short months before the Major trade-marked his pedigreed seed, the keynote speaker to the Wisconsin agricultural fair warned the farmers and scientists to beware of new technologies that distance farmers from their crops. Although his immediate concern was the steam engine's use in agriculture - he wasn't against it, just worried about whose interests it was serving - the speaker opined that the task of agricultural technology is to provide a decent living for farmers and to feed people. Clinton's administration might do well to heed Abraham Lincoln's advice before allowing the Terminator to enslave the world's farmers today.[7] Terminating the Terminator People's organizations and governments can halt the Terminator. Legal means are available through International Law and existing intergovernmental convention to outlaw the technology. Here are a few possibilities. 1. The USDA/Delta patent is pending around the world. The patent can and should be rejected on the grounds that it is in conflict with public morality. The Terminator is a threat to food security and destructive of agricultural biodiversity. On these grounds, governments are fully entitled under the terms of even the quarrelsome TRIPS chapter of the WTO (World Trade Organization) agreement to refuse the patent. In doing so, governments are also (according to the WTO) agreeing not to allow the technology to be exploited by others within their territory. 2. Pressure (within and without the United States) should be put on the USDA to refuse to surrender the patent to the company. In fact, the USDA (which surprised itself with the March 3rd patent announcement) should also petition the US Patent and Trademark Office to revisit the claims and determine whether or not it is indeed in conflict with public morality. 3. The 100+ member states to the Convention on the Prohibition of the Development, Production, and Stockpiling of Bacteriological and Toxic Weapons, and on Their Destruction (1972) should call for the abolition of Terminator Technology as a form of economic biological warfare that not only makes war on farming communities but could be manipulated to threaten national food security and destroy the national agricultural economy. 4. At its October 1998 meeting the Consultative Group on International Agricultural Research (CGIAR), the world's largest international public plant breeding network) should announce its opposition to the Terminator and its refusal to use it itself. 5. At its May 1999 meeting, the Convention on Biological Diversity's Subsidiary Body on Science and Technology should pass a resolution declaring the Terminator a threat to agricultural biodiversity and calling for its removal. Such an initiative would strengthen national efforts to ban the patent and the technology under the terms of the World Trade Agreement. Box 1. In a Terminator plant, three genes are inserted, each with an associated regulatory switch, called a 'promoter'. One of these genes, when switched on, produces a protein called Recombinase, which acts like molecular scissors [ILLUSTRATION FOR FIGURE 1B OMITTED]. The Recombinase removes a 'spacer' between the toxin-producing gene [ILLUSTRATION FOR FIGURE 1A OMITTED] and its promoter. While it is there, the spacer acts as a safety catch to prevent the toxin gene from being activated. A third gene is engineered to produce a Repressor [ILLUSTRATION FOR FIGURE 1C 4 of 6 23/11/06 15:16 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... OMITTED] which keeps the Recombinase gene turned off until the plant with the Terminator Technology is exposed to a specific outside stimulus, such as a particular chemical, temperature shock, or osmotic shock. When the chosen stimulus is applied to the seed before sale, the functioning of the Repressor gets interrupted. And as it is no longer repressed, the recombinase gene is switched on. The Recombinase that is now produced, removes the spacer 'safety catch'. Because the promoter in front of the toxin gene is chosen to only become active in the late stages of seed maturation, only then will it initiate the production of the poison that kills the seed. The preferred genes used in the Terminator Technology are: For toxin gene R.I.P. gene (ribosomal inhibitor protein) promoter LEA promoter (late embryonic abundance) spacer a stretch of DNA framed with specific recognition sites (LOX) For Recombinase gen CRE/LOX system from bacteriophage (viruses that attack bacteria) promoter a promoter that can be repressed For Repressor gene Tetracycline repressor system (Tn10 tet) Box 2. "Gene silencing" was discovered in the early nineties when, in a field of 10,000 petunias genetically-engineered to carry a uniform red gene, many of the plants were found blooming white and pink.[1] Plants are capable of deactivating genes and their promoters if recognized as intruders or as duplicates of their own DNA.[2] Furthermore, genes that have been deactivated can become active again generations later. The LEA promoter, which is used to regulate Terminator's toxin gene, is very common among plants and shows significant similarities across many species; once added, the plant might choose to switch it off. If this were to happen whilst plants were being multiplied for the commercial market, no one could tell. Seeds of such plants will eventually be treated with tetracycline; the blocking sequence [ILLUSTRATION FOR FIGURE 1A OMITTED] will be cut out but no toxin is produced at the end of the life cycle. The pollen carrying the silent but functional toxin gene could spread into neighbouring cropfields and forests. Another likely scenario is that some plants will not react to the tetracycline treatment. Consider the vast quantities of antibiotics necessary to soak millions of seeds. Who is going to check that all seeds have taken up the chemical, with a generation having to pass before results can be seen? Again pollen will spread - with all its novel genes. If down the line the Repressor passes onto one plant, but the toxin and the Recombinase pass to another, all the seeds produced by the second plant would commit suicide. Even if all three genes stay together, there might be a future chemical input that acts like tetracycline. References 1. see Steinbrecher, R.A., 1996. "From Green to Gene Revolution". The Ecologist Vol.26 No.6. pp. 273-281. 2. Kumpatla, S.P. et al. 1998. "Genome intruder scanning and modulation systems and transgene silencing", Trends in Plant Science. 3(3): pp. 97-104. Box 3.Tetracycline is a broad spectrum antibiotic. It is used in medicine to kill bacteria, but it can also affect humans if wrongly used. The soil is full of vital micro-organisms, including bacteria, on which the health of plants depend. Whilst plants will normally grow up in close partnership with soil-organisms, the tetracycline-soaked seeds could create a death zone around them, destroying the fragile balance of the microbial soil web. As a consequence farmers would have to resort to chemicals to protect their crop from disease and apply fertilizers to make them grow. The Terminator would not only deplete diversity, but also destroy soil. 5 of 6 23/11/06 15:16 Steinbrecher and Mooney, Terminator Technology http://www.gse.buffalo.edu/FAS/Bromley/classes/socprac/readings/S... References and Notes 1. Berlan, Jean-Pierre and Richard C..Lewontin. "Agricultural Genetics and Sterifix Breeding" (1998) unpublished manuscript, from an advertisement inserted at pages 5-6. 2. Lewontin, Richard C., and Berlan, Jean-Pierre, "The Political Economy of Agricultural Research: The Case of Hybrid Corn" Chapter 23, p. 625 in Carroll, Ronald, C., Vandermeer, John H., and Rossett, Peter, Agroecology, McGraw-Hill Publishing Co. 3. For further information about the new push for cereal hybrids, please see RAFI Communique "Seed Industry Consolidation - 1988: Who Owns Whom?" (July/August, 1988) at the RAFI website www.rafi.ca/ 4. Freiburg, Bill, "Is Delta and Pine Land's Terminator Gene a Billion Dollar Discover?" in Seeds and Crop Digest, May-June, 1998. 5. Collins, Harry B. "New Technologies and Modernizing World Agriculture", an unpublished paper distributed by Dr. Collins during a debate on Terminator held June 12th, 1998 during the FAO Commission on Genetic Resources for Food and Agriculture (Rome). 6. Via a Freedom of Information application to the US Army, RAFI recently received documentation from a military seminar titled, "Biotechnology Workshop 20/20" (May 29-30, 1996, held at the Army War College. The papers outline a wide range of military uses for biotechnology which the authors believe to be feasible by the year 2020. 7. Abraham Lincoln, "Annual Address by Hon. Abram Lincoln of Illinois delivered at Milwaukee, Sept. 30, 1859" pages 287-299 in Transactions of the Wisconsin State Agricultural Society. Carpenter and Hyer, (Madison) 1860. Dr. Ricarda A. Steinbrecher is a geneticist and biologist. She is coordinating the Test Tube Harvest Campaign of the Women's Environmental Network, is Science Director of the Genetics Forum, UK and is biotechnology advisor to many non-governmental organisations. Pat Roy Mooney has worked for more than 30 years with civil society organisations on international trade and development issues related to agriculture and biodiversity and is the author of several books on the subject. He lives in Winnipeg, Canada, where he is Executive Director of RAFI. Copyright © 2000, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company. 6 of 6 23/11/06 15:16