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Chapter 15 Lipids
15.1
Lipids
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Publishing as Benjamin Cummings
1
Lipids
Lipids are
 Biomolecules that contain fatty acids or a steroid
nucleus.
 Soluble in organic solvents but not in water.
 Named for the Greek word lipos, which means “fat.”
 Extracted from cells using organic solvents.
2
Types of Lipids
The types of lipids containing fatty acids are
 Waxes.
 Fats and oils (triacylglycerols).
 Glycerophospholipids.
 Prostaglandins.
 Not steroids, as they do not contain fatty acids.
3
Structures of Lipids
4
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15.2 Fatty Acids
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5
Fatty Acids
Fatty acids
 Are long-chain
carboxylic acids.
 Typically contain 12-18
carbon atoms.
 Are insoluble in water.
 Can be saturated or
unsaturated.
6
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Fatty Acid Formulas
The formulas for fatty acids are written as
 Condensed formulas.
 Line-bond formulas.
 For example caprylic acid with 8 carbon atoms.
CH3—(CH2)6—COOH
CH3—CH2—CH2—CH2—CH2—CH2—CH2—COOH
O
OH
7
Saturated Fatty Acids
Saturated fatty acids have
 Single C–C bonds.
 Molecules that fit closely together
in a regular pattern.
 Strong attractions between fatty
acid chains.
 High melting points that make
them solids at room temperature.
8
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Some Saturated Fatty Acids
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9
Unsaturated Fatty Acids
Unsaturated fatty acids
 Have one or more double C=C bond
 Typically contain cis double bonds.
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10
Properties of Unsaturated Fatty
Acids
Unsaturated fatty acids
 Have “kinks” in the fatty
acid chains.
 Do not pack closely.
 Have few attractions
between chains.
 Have low melting points.
 Are liquids at room
temperature.
“kinks” in
chain
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11
Unsaturated Fatty Acids
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12
Comparing Melting Points of
Some Fatty Acids
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13
Learning Check
Assign the melting points of –17°C, 13°C, and 69°C
to the correct fatty acid. Explain.
stearic acid (18 C) saturated
oleic acid (18 C) one double bond
linoleic acid (18 C) two double bonds
14
Solution
Stearic acid is saturated and would have a higher
melting point than the unsaturated fatty acids.
Because linoleic has two double bonds, it would have
a lower mp than oleic acid, which has one double
bond.
stearic acid mp 69°C saturated
oleic acid mp 13°C
linoleic acid mp -17°C most unsaturated
15
Prostaglandins
Prostaglandins have
 20 carbon atoms in their fatty acid chains.
 An OH on carbon 11 and 15.
 A trans double bond at carbon 13.
C 11
C 13
C 15
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16
Prostaglandins in the Body
Prostaglandins are
 Produced by injured
tissues.
 Involved in pain,
fever, and
inflammation.
 Not produced when
anti-inflammatory
drugs such as aspirin
inhibit their synthesis.
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17
Omega-6 and Omega 3- Fatty
Acids
Fatty acids
 In vegetable oils are mostly omega-6 with
the first C=C at C6.
linoleic acid
CH3─(CH2)4─CH=CH─CH2─CH=CH─(CH2)7─COOH
6
 In fish oils are mostly omega-3 with the
first C=C at C3.
linolenic acid
CH3─CH2─(CH=CH─CH2)3─(CH2)6─COOH
3
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Some Omega-6 and Omega-3
Fatty Acids
19
Learning Check
Write a fatty acid with 10 carbon atoms that is:
A. saturated
B. monounsaturated omega-3
C. monounsaturated omega-6
20
Solution
Write a fatty acid with 10 carbon atoms that is:
A. saturated
CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH
B. monounsaturated omega-3
CH3—CH2—CH=CH—CH2—CH2—CH2—CH2—CH2—COOH
C. monounsaturated omega-6
CH3—CH2—CH2—CH2—CH2—CH=CH—CH2—CH2—COOH
21
Waxes, Fats, and Oils
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22
Waxes
Waxes are
 Esters of saturated fatty acids and long-chain alcohols.
 Coatings that prevent loss of water by leaves of plants.
TABLE 17.2
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23
Fats and Oils: Triacylglycerols
Fats and oils are
 Also called triacylglycerols.
 Esters of glycerol.
 Produced by esterification.
 Formed when the hydroxyl
groups of glycerol react with the
carboxyl groups of fatty acids.
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24
Triacylglycerols
In a triacylglycerol,
 Glycerol forms ester bonds with three fatty acids.
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25
Formation of a Triacylglycerol
glycerol
+
three fatty acids
triacylglycerol
O
CH2
OH
HO C
O
(CH2)14CH3
CH
OH +
HO C
O
(CH2)14CH3
CH2
OH
HO C
(CH2)14CH3 CH2 O C
O
(CH2)14CH3
O
CH O C
(CH2)14CH3 + 3H2O
O
CH2 O C
(CH2)14CH3
26
Olive Oil
Olive oil
 Contains a high
percentage of oleic
acid, which is a
monounsaturated fatty
acid with one cis
double bond.
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27
Learning Check
What are the fatty acids in the following triacylglycerol?
O
CH2
O
C
(CH2)16CH3
O
CH
O
CH2
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
28
Solution
O
CH2
O
C
(CH2)16CH3
Stearic acid
O
CH
O
CH2
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
Oleic acid
Myristic acid
29
Melting Points of Fats and Oils
A triacylglycerol that is a fat
 Is solid at room temperature.
 Is prevalent in meats, whole milk, butter, and cheese.
A triacylglycerol that is an oil
 Is liquid at room temperature.
 Is prevalent in plants such as olive and safflower.
30
Oils with Unsaturated Fatty Acids
Oils
 Have more unsaturated fats.
 Have cis double bonds that cause “kinks” in the
fatty acid chains.
 Cannot pack triacylglycerol molecules as close
together as in fats.
 Have lower melting points than saturated fats.
 Are liquids at room temperature.
31
Diagram of Triacylglycerol with
Unsaturated Fatty Acids
Unsaturated fatty acid
chains have kinks that
do not allow close
packing.
32
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Saturated and Unsaturated Fatty
Acids In Fats and Oils
33
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Chemical Properties of
Triacylglycerols
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34
Chemical Properties of
Triacylglycerols
The chemical reactions of triacylglycerols are similar
to those of alkenes and esters.
 In hydrogenation, double bonds in unsaturated
fatty acids react with H2 in the presence of a Ni or
Pt catalyst.
 In hydrolysis, ester bonds are split by water in the
presence of an acid, a base, or an enzyme.
35
Hydrogenation of Oils
The hydrogenation of oils
 Adds hydrogen (H2) to the carbon atoms of double bonds.
 Converts double bonds to single bonds.
 Increases the melting point.
 Produces solids such as margarine and shortening.
36
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Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
Ni
O
CH
CH2
O
O
+ 3H2
C (CH2)5CH CH(CH2)7CH3
O
C
O
(CH2)5CH CH(CH2)7CH3 CH2
O
C
(CH2)14CH3
O
glyceryl tripalmitoleate
(tripalmitolean)
CH
O
CH2
O
C (CH2)14CH3
O
C
(CH2)14CH3
glyceryl tripalmitate
(tripalmitin)
37
Learning Check
What product(s) is obtained from the complete
hydrogenation of glyceryl trioleate?
1. Glycerol and 3 oleic acids
2. Glyceryltristearate
3. Glycerol and 3 stearic acids
38
Solution
What product(s) is obtained from the complete
hydrogenation of glyceryl trioleate?
2. Glyceryltristearate
39
Olestra, A Fat Substitute
Olestra is
 Used in foods as an artificial fat.
 Sucrose linked by ester bonds to several long-chain
fatty chains.
 Not broken down in the intestinal tract.
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40
Cis and Trans Fatty Acids
Unsaturated fatty acids can be
 Cis with bulky groups on same side of C=C.
CH3─ (CH2)5
(CH2)7─ COOH cis
C=C
H
H
 Trans have bulky groups on opposite sides of C=C.
CH3─ (CH2)5
H
C=C
H
trans
(CH2)7─ COOH
41
Trans Fatty Acids and
Hydrogenation
Trans fatty acids
 Are formed during hydrogenation when cis double
bonds are converted to trans double bonds.
 In the body behave like saturated fatty acids.
 Are estimated to make up 2-4% of our total
Calories.
 Are reported in several studies reported to raise
LDL-cholesterol and lower HDL-cholesterol.
42
Learning Check
(1) True or (2) False
A. There are more unsaturated fats in vegetable oils.
B. Vegetable oils have higher melting points than fats.
C. Hydrogenation of oils converts some cis-double
bonds to trans- double bonds.
D. Animal fats have more saturated fats.
43
Solution
(1) True or (2) False
A. T There are more unsaturated fats in vegetable oils.
B. F Vegetable oils have higher melting points than fats.
C. T Hydrogenation of oils converts some cis-double
bonds to trans- double bonds.
D. T Animal fats have more saturated fats.
44
Hydrolysis
In hydrolysis,
 Triacylglycerols split into glycerol and three fatty acids.
 An acid or enzyme catalyst is required.
O
CH2
CH
CH2
O
O
O
C
O
(CH2)14CH3
C (CH2)14CH3 +3H2O
O
C
(CH2)14CH3
H+
CH2 OH
CH
OH
O
+ 3 HO C
(CH2)14CH3
CH2 OH
45
Saponification and Soap
Saponification
 Is the reaction of a fat with a strong base.
 Splits triacylglycerols into glycerol and the salts of
fatty acids.
 Is the process of forming “soaps” (salts of fatty
acids).
 With KOH gives softer soaps.
46
Saponification
O
CH2 O C
(CH2)14CH3
O
CH O C
(CH2)14CH3 + 3NaOH
O
CH2 O C
CH2 OH
(CH2)14CH3
CH OH
O
+ 3 Na+ -O C (CH2)14CH3
“soap”
CH2 OH
47
Learning Check
What products are obtained from the complete
hydrolysis of glyceryl trioleate?
1. Glycerol and 3 oleic acids
2. Glyceryl tristearate
3. Glycerol and 3 stearic acids
48
Solution
What products are obtained from the complete
hydrolysis of glyceryl trioleate?
1. Glycerol and 3 oleic acids
49
Learning Check
Write the product of the following reaction.
O
CH2
O C
O
(CH2)5CH CH(CH2)7CH3
CH
O
C (CH2)5CH
O
CH2
O
C
(CH2)5CH
CH(CH2)7CH3 + 3 H2
Ni
CH(CH2)7CH3
50
Solution
O
CH2
O
C (CH2)14CH3
O
CH
O
C (CH2)14CH3
O
CH2
O
C
(CH2)14CH3
51
Glycerophospholipids
Glycerophospholipids are
 The most abundant lipids in cell membranes.
 Composed of glycerol, two fatty acids, phosphate
and an amino alcohol.
Fatty acid
Glycerol
Fatty acid
PO4
Amino
alcohol
52
Glycerophospholipids Are Polar
A glycerophospholipid has
 Two nonpolar fatty acid chains.
 A phosphate group and a polar amino alcohol.
CH3
│+
+
HO−CH2−CH2−N−CH3
HO−CH2−CH2−NH3
│
choline
CH3
ethanolamine
+
NH3
│
HO−CH2−CH−COO−
serine
Amino alcohols
53
Structure and Polarity of A
Glycerophospholipid
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54
Lecithin and Cephalin
Lecithin and cephalin are glycerophospholipids
 Abundant in brain and nerve tissues.
 Found in egg yolk, wheat germ, and yeast.
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55
Learning Check
Identify each as a
A. fatty acid
C. amino alcohol
B. triacylglycerol
D. glycerophospholipid
1. glyceryl trioleate
2. cephalin
3. choline
4. palmitic acid
56
Solution
Identify each as a
A. fatty acid
C. amino alcohol
1. glyceryl trioleate
2. cephalin
3. choline
4. palmitic acid
B. triacylglycerol
D. glycerophospholipid
B. triacylglycerol
D. glycerophospholipid
C. amino alcohol
A. fatty acid
57
Learning Check
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│
O58
Solution
Identify the components and type of glycerophospholipid
O
║
CH2−O −C −(CH2)16 −CH3
O
║
CH2−O −C −(CH2)16 −CH3
2 stearic acids
+
O
NH3
║
│
CH2−O −P −O − CH2−CH−COO│
serine
Ophosphate
amino alcohol
type = cephalin
59
Sphingolipids
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Sphingolipids
Sphingolipids
 Are similar to phospholipids.
 Contain sphingosine (a long-chain amino alcohol), a
fatty acid, phosphate, and a small amino alcohol.
 Have polar and nonpolar regions.
fatty acid
sphingosine
PO4
amino
alcohol
61
Sphingosine
Sphingosine is a long-chain unsaturated amino alcohol.
CH3−(CH2)12 −CH=CH−CH−OH
│
CH−NH2
│
CH2−OH
sphingosine
62
Sphingolipids
In sphingomyelin, a sphingolipid found in nerve cells
 There is an amide bond between a fatty acid and
sphingosine, an 18-carbon alcohol.
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63
Glycosphingolipids
 Glycosphingolipids
contain
monosaccharides
bonded to the –OH
of sphingosine by a
glycosidic bond.
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64
Glycosphingolipids and
Cerebrosides
Glycosphingolipids
 Are sphingolipids that contain
monosaccharides.
 Can be a cerebroside with galactose.
65
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Gangliosides
Gangliosides
 Are similar to cerebrosides, but contain two or
more monosaccharides.
 Are important in neurons.
 Act as receptor for hormones and viruses.
 Can accumulate and cause genetic diseases.
66
Gangliosides
GM2 is a ganglioside
 That accumulates in Tay-Sachs disease.
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67
Lipid Diseases (Lipidoses)
 In many lipid diseases, the deficiency of an enzyme
causes the accumulation of glycolipids.
TABLE 17.3
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68
Learning Check
Identify each as a
1) Fatty acid
2) Triacylglycerol
3) Amino alcohol
4) Glycerophospholipid
5) Glycosphingolipid
A. Glyceryl trioleate
B. Cephalin
C. Choline
D. Galactocerebroside
E. Palmitic acid
69
Solution
A. Glyceryl trioleate
B. Cephalin
C. Choline
D. Galactocerebroside
E. Palmitic acid
2) Triacylglycerol
4) Glycerophospholipid
3) Amino alcohol
5) Glycosphingolipid
1) Fatty acid
70
Steroids: Cholesterol, Bile Salts,
and Steroid Hormones
CH3
CH3
CH3
CH3
CH3
HO
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Steroid Nucleus
A steroid nucleus consists of
 3 cyclohexane rings.
 1 cyclopentane ring.
 No fatty acids.
steroid nucleus
72
Cholesterol
Cholesterol
 Is the most abundant steroid in the body.
 Has methyl CH3- groups, alkyl chain, and -OH
attached to the steroid nucleus.
CH3
CH3
CH3
CH3
CH3
HO
73
Cholesterol in the Body
Cholesterol in the body
 Is obtained from meats,
milk, and eggs.
 Is synthesized in the liver.
 Is needed for cell
membranes, brain and
nerve tissue, steroid
hormones, and Vitamin D.
 Clogs arteries when high
levels form plaque.
A normal, open artery.
An artery clogged by
cholesterol plaque
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Cholesterol in Foods
Cholesterol is
 Synthesized in
the liver.
 Obtained from
foods.
 Considered
elevated if
plasma
cholesterol
exceeds 200
mg/dL.
TABLE 17.4
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75
Learning Check
Match the components of the cholesterol molecule with
the following:
___ carbon chain
___hydroxyl group
___ steroid nucleus
___methyl group
D
B
CH3
CH3
CH3
CH3
CH3
A
C
HO
76
Solution
Match the components of the cholesterol molecule with
the following:
D carbon chain
A hydroxyl group
C steroid nucleus
B methyl group
D
B
CH3
CH3
CH3
CH3
CH3
A
C
HO
77
Bile Salts
Bile salts
 Are synthesized in the liver from cholesterol.
 Are stored in the gallbladder.
 Are secreted into the small intestine.
 Have a polar and a nonpolar region
 Mix with fats to break them part.
 Emulsify fat particles to provide large surface area.
78
Bile Salts
glycine, an amino acid
cholic acid, a bile acid
CH3
OH
CH3
O
C
CH2
N
H
COO- Na+
Polar region
CH3
HO
OH
Nonpolar region
sodium glycocholate, a bile salt
79
Lipoproteins
Lipoproteins
• Combine lipids with proteins and phospholipids.
• Are soluble in water because the surface consists of
polar lipids.
80
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Types of Lipoproteins
Lipoproteins
 Differ in density, composition, and function.
 Include low-density lipoprotein (LDLs) and highdensity lipoprotein (HDLs).
TABLE 17.5
81
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Transport of Lipoproteins in
the Body
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82
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.
83
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Adrenal Corticosteroids
Adrenal corticosteroids are steroid hormones that
 Are produced by the adrenal glands located on
the top of each kidney.
 Include aldosterone, which regulates electrolytes
and water balance by the kidneys.
 Include cortisone, a glucocorticoid, which
increases blood glucose level and stimulates the
synthesis of glycogen in the liver.
84
Adrenal Corticosteroids
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85
Anabolic Steroids
Anabolic steroids
 Are derivatives of testosterone.
 Are used illegally to increase muscle mass.
 Have side effects including fluid retention, hair growth,
sleep disturbance, and liver damage.
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86
Learning Check
Identify each as a
1. fatty acid
2. steroid
3. triacylglycerol
4. phospholipid
5. sphingolipid
A. cholesterol
B. glycerol, 2 fatty acids, phosphate, and choline
C. glyceryl tristearate
D. sphingosine, fatty acid, phosphate, and choline
E. estradiol
F. bile salts
G. lipids in plasma membranes
87
Solution
A.
B.
C.
D.
E.
F.
G.
cholesterol
2 steroid
glycerol, 2 fatty acids, phosphate, and choline
4 phospholipid
glyceryl tristearate
3 triacylglycerol
sphingosine, fatty acid, phosphate, and choline
5 sphingolipid
estradiol 2 steroid
bile salts 2 steroid
lipids in plasma membranes
4 phospholipid, 5 sphingolipid
.
88
Cell Membranes
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Cell Membranes
Cell membranes
 Separate cellular contents from the external
environment.
 Consist of a lipid bilayer made of two rows of
phospholipids.
 Have an inner portion made of the nonpolar tails of
phospholipids with the polar heads at the outer
and inner surfaces.
90
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.
91
Fluid Mosaic Model
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Transport 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.
 Active transport, which moves ions against a
concentration gradient.
93
Transport Pathways Through Cell
Membranes
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94
Learning Check
The transport of particles across a cell membrane from
high concentration to low concentration is called
1. Facilitated transport
2. Diffusion
3. Active transport
95
Solution
The transport of particles across a cell membrane from
high concentration to low concentration is called
2. Diffusion
96