15.1 Intro to Lipids
Lipids are biochemical molecules that are
insoluble or sparingly soluble in water, but
are soluble in nonpolar organic solvents.
Uses of lipids:
Storage of energy
Insulation
Protection from mechanical damage
Major component of cell membranes
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15.1 Intro to Lipids
Types of lipids:
I.
Saponifiable lipids contain fatty acids
bound as esters. Saponification (soapmaking) is hydrolysis of the esters and
frees the fatty acids. These lipids can
be classified as polar or nonpolar.
II.
Nonsaponifiable lipids do not contain
fatty acids bound as esters.
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15.2 Structures of Fatty Acids
Fatty acids are carboxylic acids with unbranched hydrocarbon chains. They
contain an even number of carbon atoms.
Fatty acids can be
saturated: contain no double bonds
monunsaturated: contain one double bond
polyunsaturated: contain several double
bonds
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15.2 Structures of Fatty Acids
The double bonds in naturally-occurring fatty
acids have cis double bonds. These put
kinks in the hydrocarbon backbone.
Two of the polyunsaturated fatty acids are
essential in the diet; they cannot be synthesized by the body. Both contain 18
carbon atoms. Fish and vegetable oils are
dietary sources of these fatty acids.
Linoleic acid (2 double bonds)
Linolenic acid (3 double bonds)
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15.2 Structures of Fatty Acids
Stearic acid
Oleic acid
Linoleic acid
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Linolenic acid
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15.2 Structures of Fatty Acids
O
C
OH
Stearic acid, a saturated fatty acid
OH
C
Oleic acid, a monounsaturated fatty acid
O
OH
Linoleic acid, an -6 polyunsaturated acid
C
O
OH
Linolenic acid, an -3 polyunsaturated acid
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C
O
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15.3 Properties of Fatty Acids
The melting
points of fatty
acids depend
on the number of carbon
atoms and
the degree of
unsaturation.
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15.3 Properties of Fatty Acids
The bent shapes of unsaturated fatty acids prevent them from fitting together and forming
high-melting solids.
Fatty acids with trans double bonds are found
in “trans fats.” The trans double bonds are
formed when vegetable oils are processed.
These fatty acids have higher melting points
than the cis isomers.
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15.3 Properties of Fatty Acids
Melting points:
70C
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13C
45C
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15.4 Triglycerides
Triglycerides are triesters. They are products
of the reaction of glycerol and fatty acids.
They are also called triacylglycerols, and are
the nonpolar saponifiable lipids.
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15.4 Triglycerides
Simple triglycerides contain three identical
fatty acids. Mixed triglycerides contain
three different fatty acids.
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15.4 Triglycerides
Triglycerides are the most abundant lipids,
and are used for storage of energy.
Solid or semisolid triglycerides are called
fats. They contain mainly saturated fatty
acids. They are found in meats and
tropical nuts.
Liquid triglycerides are called fats. They
contain mainly unsaturated fatty acids.
They are found in fish and plants.
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15.4 Triglycerides
The kinks associated with unsaturated fatty
acids prevent the molecules from packing
neatly and forming solids.
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15.4 Triglycerides
Fatty acid contents of common fats and oils.
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15.5 Reactions of Triglycerides
Complete hydrolysis of triglycerides produces
the triol, glycerol, and free fatty acids.
Triglyceride + 3 H2O
Glycerol + 3 Fatty Acids
Metabolic hydrolysis requires enzymes from
the pancreas. Usually, two of the fatty acids
are hydrolyzed, leaving a monoglyceride.
Triglyceride + 2 H2O
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Monoglyceride
+ 2 Fatty Acids
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15.5 Reactions of Triglycerides
Saponification is hydrolysis of triglycerides in
basic solution. The fatty acid is obtained as
its carboxylate salt, or soap.
Triglyceride + 3 OH1
Glycerol + 3 Carboxylates
The carboxylate anion has a polar end and a
nonpolar hydrocarbon chain. The polar end
is hydrophilic (water-loving) and the nonpolar chain is hydrophobic (water-fearing.)
nonpolar "tail"
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O
C
polar
O "head"
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15.5 Reactions of Triglycerides
The two parts of the molecules associate
to form micelles and other structures.
From Wikipedia
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15.6 Phosphoglycerides
Phosphoglycerides are polar saponifiable
lipids. Two of the alcohols on glycerol
are esterified with fatty acids. The third
is esterified with phosphoric acid, which
is esterified with an aminoalcohol.
O
O
R2
C
O
CH2 O
C
CH
O
CH2 O
P
R1
O
R3
O
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15.6 Phosphoglycerides
CH3
Phosphatadylcholines,
a.k.a. lecithins,
Different
types of
contain choline
HO CH2 CH2 N CH3
phosphoglycerides
contain different aminoalcohols.CH3
H
HO
CH2 CH2 N
Cephalins contain
ethanolamine
or serine
H
H
HO
CH2 CH
N
C
O
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H
H
H
O
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15.6 Phosphoglycerides
The phosphate ester of lecithins is quite
polar. It has a charged phosphate group
and a quaternary amine.
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15.6 Phosphoglycerides
A space-filling drawing shows its polar head
and two nonpolar tails.
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15.6 Phosphoglycerides
Phosphatidylcholines form micelles and are
good emulsifiers.
They are major components of cell membranes.
They are abundant in egg yolk and soybeans.
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15.6 Phosphoglycerides
Cephalins are found in heart, liver, and brain
tissue.
They are important in the clotting of blood.
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15.7 Sphingolipids
Sphingolipids are polar saponifiable lipids
based on sphingosine rather than glycerol.
H
CH3 (CH2)12 C
C
H
CH
OH
CH
NH2
CH2 OH
A fatty acid is bonded to the nitrogen as
an amide.
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15.7 Sphingolipids
Sphingomyelins contain a phosphate ester
bonded to choline.
H
CH3 (CH2)12 C
C
H
CH
OH
O
CH
NH
C
R
CH2
O
O
P
O
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CH3
O
CH2 CH2 N
CH3
CH3
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15.7 Sphingolipids
Sphingomyelins are found in cell membranes,
and are important structural components of
the myelin sheath of nerves.
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15.7 Sphingolipids
Cerebrosides contain a monosaccharide
rather than a phosphate.
H
CH3 (CH2)12 C
C
H
CH2OH
OH
O
OH
Galactose
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O
CH
OH
O
CH
NH
C
R
CH2
Glycoside linkage
OH
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15.8 Steroids
Steroids are nonsaponifiable lipids
that possess the steroid skeleton.
C
A
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D
B
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15.8 Steroids
Cholesterol is the most abundant
steroid in the human body.
CH3
H3C
CH3
CH3
CH3
H
H
H
HO
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15.8 Steroids
Cholesterol is the most abundant
steroid in the human body.
CH3
H3C
CH3
CH3
H
CH3
H
H
H
HO
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15.8 Steroids
Cholesterol is the most
abundant steroid in the
human body.
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15.8 Steroids
Cholesterol, when mixed with a fat or
oil, enables the substance to absorb a
fair amount of water.
Cholesterol is abundant in wool fat,
a.k.a. lanolin.
Cholesterol is used as a grease vehicle
in ointments when water-soluble components are required.
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15.8 Steroids
Cholesterol is a precursor to
other important steroids
Bile salts
Hormones
Vitamin D
Cholesterol is a risk factor for
atherosclerosis, a buildup of
plaque, in the arteries.
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15.8 Steroids
Bile salts have a polar group at the end of the
hydrocarbon at carbon 17. They emulsify
lipids in the digestive system.
H3C
O
CH3
H
CH3
H
HO
H
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H
H
N
H
O
O
OH sodium glycocholate
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15.8 Steroids
Hormones are messenger molecules
produced in ductless glands. They
are carried to specific tissues where
they trigger a response.
Steroid hormones regulate “sugar, salt,
and sex!”
Adrenocortical steroids regulate sugar
and salt. They are secreted by the
adrenal glands. Some are used as
anti-inflammatory drugs.
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15.8 Steroids
Hormones are messenger
molecules produced in
ductless glands. They are
carried
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15.8 Steroids
Estrogens are steroid hormones that cause
development of secondary sex characteristics
in females and regulate the menstrual cycle.
Progestins are steroid hormones that regulate
pregnancy.
Androgens promote development of secondary
sex characteristics in males and promote
muscle growth. They are sometimes called
anabolic steroids.
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15.8 Steroids
Estrogens are steroid hormones that cause
development of secondary sex characteristics
in females and regulate the menstrual cycle.
Progestins are steroid hormones that regulate
pregnancy.
Androgens promote development of secondary
sex characteristics in males and promote
muscle growth.
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15.8 Steroids
Many synthetic steroids are available as drugs.
Anabolic steroids cause the body to increase
protein synthesis, especially in the muscles.
They also prevent the breakdown of muscle
tissue and affect cell differentiation, favoring
muscle over fat cells.
Side effects include acne, liver disease, infertility, and development of inappropriate secondary sex characteristics. They can stunt
growth in puberty and affect sex characteristics of unborn infants.
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15.8 Steroids
Tamoxifen and raloxifene are selective
estrogen receptor modulators, a.k.a.
SERMs, that block estrogen receptors
and slow or prevent growth of breast
cancer.
HO
O
O
N
N
S
O
Tamoxifen
(NolvadexTM)
Raloxifene (EvistaTM)
HO
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15.8 Steroids
Diethylstilbestrol, a.k.a. DES, was used in
1940’s and 1950’s to prevent miscarriage.
It caused vaginal cancer in daughters of
women who took it. (Rare)
It caused premature labor in daughters of
women who took it. (Common)
OH
HO
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Prostaglandins
Prostaglandins are lipids derived from
arachidonic acid.
They were first isolated from prostate
glands.
Prostaglandins have hormone-like properties and are involved in inflammation.
Aspirin blocks production of
prostaglandins.
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Prostaglandins
O
Prostaglandins are lipids
derived from
C
OH
arachidonic
acid
arachidonic acid. They
have
hormoneCH3
like properties. They are involved in
inflammation; aspirin blocks production
O
of prostaglandins.
OH
C
O
HO
PGF2
CH3
OH
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15.9 Cell Membranes
Cell membranes separate the aqueous
environment inside the cell from the
external aqueous environment.
The membrane also controls movement
of substances into and out of the cell.
Phospholipids are a major component of
cell membranes. They form lipid
bilayers.
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15.9 Cell Membranes
The membrane also controls movement
of substances into and out of the cell.
Phospholipids are a major component of
cell membranes. They form lipid
bilayers.
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15.9 Cell Membranes
The kinks associated with cis double bonds
in fatty acid chains prevent tight packing
of the lipid molecules in a lipid bilayer.
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15.9 Cell Membranes
Cholesterol molecules fit between fatty acid
chains in a lipid bilayer. They regulate the
rigidity of the structure.
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15.9 Cell Membranes
Proteins are also components of the membrane.
They help move nutrients, and act as receptors
for hormones and neurotransmitters.
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