Hydrolysis

Hydrolysis
In acid or enzyme hydrolysis,
• water adds to the ester bonds.
• triacylglycerols hydrolyze forming glycerol and three fatty
acids.
• a strong acid, such as HCl or H2SO4, or an enzyme catalyst
is required.
Base Hydrolysis (Saponification )
In base hydrolysis (saponification),
• a triacylglycerol reacts with heat and a strong base.
• a triacylglycerol splits into glycerol and the salts of fatty
acids (soap).
• a solid soap that can be molded into a desired shape is
produced when NaOH is used.
• a softer, liquid soap is produced when KOH is used.
• polyunsaturated oils produce softer soaps.
Saponification
Fat or oil + strong base
glycerol + salts of fatty acids (soap)
For Lab Today
http://www.ediblegeography.com/multifunctional-desserts/
For Lab Today
• the cottonseed oil contains:
– 50% linoleate
– 30% oleate
– 20% palmitate
Summary of Organic and Lipid
Reactions
Phosphoric Acid
• Has a structure similar to carboxylic acid:
O
R
C
O
OH
HO
P
OH
OH
carboxylic acid
phosphoric acid
O
O
HO
P
OH
+
H+, heat
H-O-CH2CH3
OH
OH
phosphoric acid
HO-P-O-CH2CH3 +
methanol
methyl ethanoate
H-O-H
Glycerophospholipids
Glycerophospholipids, the
most abundant lipids in cell
membranes, contain
• two fatty acids, which form ester
bonds with the first and second
hydroxyl group of glycerol.
• a third hydroxyl group, which
forms an ester with phosphoric acid,
which then forms another
phosphoester bond with an amino
alcohol.
Insert picture
of glycerophospholipid
pg 618
Glycerophospholipids Contain
Amino Alcohols.
• Three amino alcohols found in glycerophospholipids are
choline, serine, and ethanolamine.
• In the body, at a physiological pH of 7.4, these amino
alcohols are ionized.
Insert structures of amino alcohols pg 618 bottom
Glycerophospholipids are Polar
and Nonpolar.
Glycerophospholipids have
• both polar and nonpolar regions that allow them to interact
with polar and nonpolar substances.
• an ionized amino alcohol and phosphate portion, called
―the head,‖ which is polar and strongly attracted to water.
• a hydrocarbon chain known as ―the tail,‖ which is soluble
in nonpolar substances.
Formation of
Glycerophospholipids
The formation of a glycerophospholipid occurs when ester
bonds form between glycerol and two fatty acids, and two
phosphoester bonds form between phosphoric acid and an
ionized amino alcohol and glycerol, such as palmitic acid.
Components of
Glycerophospholipids
The components of a glycerophospholipid are choline,
phosphoric acid, glycerol, and two fatty acids.
Insert structure from figure 17.6a
Components of
Glycerophospholipids
In a glycerophospholipid, a polar ―head‖ contains the ionized
amino alcohol and phosphate, while the hydrocarbon chains
of two fatty acids make up the nonpolar ―tails.‖
Learning Check
Identify the components of glycerophospholipid.
O
║
CH2—O—C— (CH2)16—CH3
O
║
CH2—O—C— (CH2)16—CH3
+
O
NH3
║
│
CH2—O—P—O—CH2—CH−COO –
│
O–
Solution
Identify the components and type of glycerophospholipid.
O
║
CH2—O—C— (CH2)16—CH3
O
║
CH2—O—C— (CH2)16—CH3
+
O
NH3
║
│
CH2—O—P—O—CH2—CH−COO –
│
Serine
O–
Phosphate
Amino alcohol
2 Stearic acids
Steroid Nucleus
Steroid molecules contain a steroid
nucleus with
• 3 cyclohexane rings,
• 1 cyclopentane ring,
• no fatty acids, and
• a total of four rings A, B, C, D.
The steroid nucleus is numbered
from the carbon atoms in ring A to
two methyl groups at 18 and 19.
Cholesterol
Cholesterol
• is the most important and abundant steroid in the
body.
• is a sterol because it contains an oxygen atom as a
hydroxyl group, –OH on carbon 3.
• has a double bond between carbon 5 and carbon 6.
• has methyl –CH3 groups, at carbon 10 and 13.
• has a carbon chain at carbon 17.
Cholesterol
Cholesterol is a component of cellular membranes,
myelin sheaths, and brain and nerve tissues.
Cholesterol in the Body
Cholesterol in the body
A normal, open artery.
• is obtained from meats, milk,
and eggs and synthesized in
the liver.
• clogs arteries when high levels
form plaque.
An artery clogged by
cholesterol plaque
Cholesterol in Foods
A typical American diet includes 400–500 mg of cholesterol
per day.
The American Heart Association has recommended no more
than 300 mg of cholesterol per day.
Saturated fats in the diet may stimulate the production of
cholesterol by the liver.
Learning Check
Match the components of the cholesterol molecule with
each of the following:
alkyl chain
hydroxyl group
steroid nucleus
methyl group
D
B
CH3
CH3
CH3
CH3
A
HO
CH3
C
Solution
Match the components of the cholesterol molecule with
each of the following:
D alkyl chain
A hydroxyl group
B methyl group
C steroid nucleus
D
B
CH3
CH3
CH3
CH3
A
HO
CH3
C
Bile Salts
Bile salts
• are synthesized from cholesterol in the liver.
• are stored in the gallbladder and secreted into the small
intestine.
• have a polar and a nonpolar region.
• help in the absorption of cholesterol into the intestinal
mucosa.
Sodium Glycocholate, a Bile Salt
Polar region
Nonpolar region
Gallstones
Gallstones are
• formed when large amounts of cholesterol accumulate in
the gallbladder.
• composed of almost 100% cholesterol, with some calcium
salts, fatty acids, and glycerophospholipids.
Hydrophobic Lipids and Biology
1.
Lipid molecules will aggregate to minimize their contact
with water.
2.
Depending on the general shape of the lipid molecule,
different-shaped aggregates form.
3.
Smaller lipids like fatty acids will come together to make
micelles.
Complex lipids
Fatty acids
If the fatty acid is shown as depicted below, then a
micelle can be visualized as….
CH3(CH2)nCOOH
hydrophobic hydrophilic
Hydrophilic
Hydrophobic
Cutaway of a micelle with the hydrophobic chains extend to the
center of this aggregate and hydrophilic groups to the outside
More complex lipids such as phospholipids
and sphingolipids are shaped differently than
fatty acids and will aggregate differently in
water solutions. They form liposomes……
hydrophilic
hydrophobic
Liposomes: Form from Phospholipids
andSphingolipids
CH3(CH2)10
H3C
H3C
N
O
O
P
CH3
O
NH
OH
O
O
(CH2)12CH3
CH3
O
O
O
O
O
O
P
O O
CH3
A cutaway of a single liposome with the bilayer
shell and the water solution core.
Lipoproteins
Lipoproteins
• are spherical particles with an outer surface of polar
proteins and glycerophospholipids that surround hundreds
of nonpolar molecules of triacylglycerols and cholesteryl
esters.
• combine lipids with proteins and phospholipids.
• are soluble in water because the surface consists of polar
lipids.
Lipoproteins
A spherical lipoprotein particle surrounds nonpolar lipids with
polar lipids and protein for transport to body cells.
Types of Lipoproteins
Lipoproteins differ in density, composition, and function
and include
• chylomicrons, very low-density lipoprotein (VLDLs);
• low-density lipoproteins (LDLs), which carry cholesterol
to the tissues; and
• high-density lipoproteins (HDLs) that pick up cholesterol
from the tissues and carry it to the liver.
LDLs
LDLs
• transport cholesterol to tissues where it can be used for
synthesis of cell membranes and steroid hormones.
• deposit cholesterol in the arteries in the form of plaque
when cholesterol levels exceed levels needed by tissues.
• called ―bad‖ cholesterol for their contribution to heart
disease.
HDLs
HDLs
• are more dense than LDLs due to the increased amount of
protein present.
• pick up cholesterol from the tissues and carry it to the liver,
where it can be converted to bile salts, which are eliminated
from the body,
• are called ―good‖ cholesterol.
VLDLs
VLDLs carry the triacylglycerols synthesized in the liver to the
adipose tissues for storage.
Insert fig 17.10 pg 626
Lipid distribution system through the bloodstream
•VLDL: very low density lipoprotein are transport vehicles for cholesterol
and lipids. Prepared by liver to move cholesterol and lipids around the body.
•LDL: smaller version of VLDL to move cholesterol and lipids to peripheral
tissues (bad guy)
•HDL: high density lipoprotein is the bloodstreams scavenger or cholesterol
vacuum cleaner (good guy)
Lipid Panel
A lipid panel is a blood test that measures serum lipid
levels including
• cholesterol
• triglycerides
• high-density lipoprotein (HDL)
• low-density lipoprotein (LDL)
The results of a lipid panel are used to evaluate a
patient’s risk of heart disease.
Lipid Panel
Steroid Hormones
Steroid hormones
• are chemical messengers in cells.
• are produced from cholesterol.
• include sex hormones, such as androgens (testosterone)
in males and estrogens (estradiol) in females.
Steroid Hormones
Learning Check
Identify each of the following as a steroid, triacylglycerol,
phospholipid, or sphingolipid.
A. cholesterol
B. glycerol, 2 fatty acids, phosphate, and choline
C. glyceryl tristearate
D. bile salts
E. lipids in plasma membranes
Solution
A. cholesterol
B. glycerol, 2 fatty acids,
phosphate, and choline
C. glyceryl tristearate
D. bile salts
E. lipids in plasma
membranes
steroid
phospholipid
triacylglycerol
steroid
phospholipid
Cell Membranes
Cell membranes have a lipid bilayer that
• separates cellular contents from the external environment.
• contains two layers of glycerophospholipids arranged with
their hydrophilic heads at the outer and inner membrane
surfaces and their hydrophobic tails in the center.
Fluid Mosaic Model of Cell
Membranes
The lipid bilayer
• contains proteins, carbohydrates, and cholesterol.
• has unsaturated fatty acids that make cell membranes
fluid-like rather than rigid.
• has proteins and carbohydrates on the surface that
communicate with hormones and neurotransmitters.
Fluid Mosaic Model
Transport Pathways Through
Cell Membranes
The transport of substances through cell membranes
involves
• diffusion (passive transport), which moves particles
from a higher to a lower concentration;
• facilitated transport, which uses protein channels to
increase the rate of diffusion; and
• active transport, which moves ions against a
concentration gradient.
Transport Pathways Through
Cell Membranes
Learning Check
What is the transport of particles across a cell membrane
from high concentration to low concentration called?
A. facilitated transport
B. diffusion (passive transport)
C. active transport
Solution
What is the transport of particles across a cell membrane
from high concentration to low concentration called?
A. facilitated transport
B. diffusion (passive transport)
C. active transport