Download Fatty Acids

Chapter 17 Lipids
17.1
Lipids
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
LIPID
Lipids:
1.
Fatty acids
2.
Neutral fats and oils
3.
Waxes
4.
Phospholipid
5.
Sterols
6.
Fat soluble vitamins
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.
3
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.
4
Structures of Lipids
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Chapter 17 Lipids
17.2 Fatty Acids
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Publishing as Benjamin Cummings
6
Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents.
Most membrane lipids are amphipathic, having a non-polar end and a polar
end.
Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.
-
A 16-C fatty acid: CH3(CH2)14 COO
-
Non-polar
polar
A 16-C fatty acid with one cis double bond between
represented as 16:1 cis D9.
C atoms 9-10 may be
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
8
Fatty Acids
O
R C OH
#1 Carbon
O
R C OH
Acid Group
Polar End - Hydrophilic End
Non-polar End - Hydrophobic End
(Fat-soluble tail)
Fatty Acids
Fatty acids
• Are long-chain
carboxylic acids.
• Typically contain 1218 carbon atoms.
• Are insoluble in
water.
• Can be saturated or
unsaturated.
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10
Saturated Fatty Acids
8
7
CH3 CH2
O
5
3
4
6
2
1
CH2 CH2 CH2 CH2 CH2 C OH
Octanoic Acid
Unsaturated Fatty Acids
8
CH3
7
CH2
5
6
CH2 CH2
4
CH2
O
3
2
1
CH2 CH2 C
OH
3 - Octenoic Acid
8
7
CH3 CH2
O
5
3
4
6
2
1
CH2 CH2 CH2 CH2 CH2 C OH
3, 6 - Octadienoic Acid
Short hand:
8:1 (D3)
8:2 (D3,6)
Cis And Trans Fatty Acids
H
H
CH3 (CH2 )7 C C (CH2 )7
10 9
O
C OH
Cis 9 - Octadecenoic Acid (oleic)
H
CH3 (CH2 )7
O
C C
(CH2 )7
C OH
H
Trans 9 - Octadecenoic Acid (elaidic acid)
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.
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14
Some Saturated Fatty Acids
TABLE 17.1
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15
Unsaturated Fatty Acids
Unsaturated fatty acids
• Have one or more double C=C
bond
• Typically contain cis double
bonds.
16
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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17
Polyunsaturated Fatty Acids
Linoleic acid:
Linolenic acid:
Cis, cis, 9, 12 - Octadecadienoic acid
Cis, cis, cis 9, 12, 15 - Octadecatrienoic acid
Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 - Eicosatetraenoic
acid
Linoleic Acid
Linolenic Acid
Arachidonic Acid
Double bonds in fatty acids
usually have the cis
configuration.
Most naturally occurring fatty
acids have an even number of
carbon atoms.

4

O
a
3
2
C
1
O
fatty acid with a cis-D9
double bond
Some fatty acids and their common names:
14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid;
18:1 cisD9 oleic acid
18:2 cisD9,12 linoleic acid
18:3 cisD9,12,15 a-linonenic acid
20:4 cisD5,8,11,14 arachidonic acid
Comparing Melting Points of Some
Fatty Acids
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20
Effects of Double Bonds on the Melting Points
Fatty. Acids.
16:0
16:1
18:0
18:1
18:2
18:3
20:0
20:4
Melting point. P. (0C)
60
1
63
16
-5
-11
75
-50
Melting Points and Solubility in Water of Fatty Acids
Melting Point
Solubility in H O
Chain Length
2
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
23
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
24
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
25
Some Omega-6 and Omega-3
Fatty Acids
26
Learning Check
Write a fatty acid with 10 carbon atoms
that is:
A. saturated
B. monounsaturated omega-3
C. monounsaturated omega-6
27
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
28
Prostaglandin: One of a number of hormone-like
substances that participate in a wide range of
body functions such as the contraction and
relaxation of smooth muscle, the dilation and
constriction of blood vessels, control of blood
pressure, and modulation of inflammation.
Prostaglandins are derived from a chemical called
arachidonic acid
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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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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31
Chapter 17
Lipids
17.3
Waxes, Fats, and Oils
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32
Waxes
Waxes are
• Esters of saturated fatty acids and long-chain
alcohols.
TABLE 17.2
• Coatings that prevent loss of water by leaves
of plants.
33
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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34
Glycerophospholipids
Glycerophospholipids
(phosphoglycerides), are common
constituents of cellular membranes.
They have a glycerol backbone.
Hydroxyls at C1 & C2 are esterified
to fatty acids.
An ester forms when a
hydroxyl reacts with a
carboxylic acid, with loss
of H2O.
CH2OH
H
C
OH
CH2OH
glycerol
Formation of an ester:
O
R'OH + HO-C-R"
O
R'-O-C-R'' + H2O
FAT AND OILS
Mostly Triglycerides:
O
HO C R
O
H2 C OH
HC OH
H2 C OH
Glycerol
+
HO C R
O
HO C R
3 Fatty Acids
O
H2 C O C R
O
HC O C R
O
H2 C O C R
+ 3 H2O
37
Triacylglycerols
In a triacylglycerol,
• Glycerol forms ester bonds with three
fatty acids.
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38
Formation of a Triacylglycerol
glycerol +
three fatty acids
triacylglycerol
O
CH2
OH
HO C
O
(CH2)14CH3
CH
OH +
HO C
O
(CH2)14CH3
HO C
(CH2)14CH3 CH2 O C
CH2
OH
O
(CH2)14CH3
O
CH O C
(CH2)14CH3 + 3H2O
O
CH2 O C
(CH2)14CH3
39
GLYCERIDES
O
H2 C OH
HC
H2 C O C (CH 2 )16 CH3
OH O
H2 C O C (CH2 )16 CH3
Monoglyceride (a - monostearin)
H2 C
HC
H2 C
HC
OH O
H2 C O C (CH 2 )16 CH3
Diglyceride (a, a' - distearin)
O
O C (CH2 )16 CH3
O
O C (CH2 )14 CH3
O
O C (CH2 )16 CH3
( C18 )
(C16 )
(C18 )
Triglyceride ( - palmityl distearin)
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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41
Learning Check
What are the fatty acids in the following
triacylglycerol?
O
CH2
O
C
(CH2)16CH3
O
CH
CH2
O
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
42
Solution
O
CH2
O
C
(CH2)16CH3
Stearic acid
O
CH
CH2
O
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
Oleic acid
Myristic acid
43
MELTING POINTS OF TRIGLYCERIDES
Triglyceride
Melting Point (°C)
C6
-15
C12
15
C14
33
C16
45
C18
55
C18:1 (cis)
-32
C18:1 (trans)
15
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.
45
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.
46
Diagram of Triacylglycerol with
Unsaturated Fatty Acids
Unsaturated fatty acid
chains have kinks that
do not allow close
packing.
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47
Saturated and Unsaturated Fatty
Acids In Fats and Oils
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48
Chapter 17
Lipids
17.4
Chemical Properties of Triacylglycerols
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49
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.
50
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.
51
Hydrogenation
O
CH2
O
C
(CH2)5CH CH(CH2)7CH3
Ni
O
CH
CH2
O
O
C (CH2)5CH
O
C
+ 3H2
CH(CH2)7CH3
(CH2)5CH CH(CH2)7CH3
glyceryl tripalmitoleate
(tripalmitolean)
O
CH2
O
C
(CH2)14CH3
O
CH
O
C (CH2)14CH3
O
glyceryl tripalmitate
CH2 (tripalmitin
O C ) (CH2)14CH3
52
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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53
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
54
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.
55
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 cisdouble bonds to trans- double bonds.
D. Animal fats have more saturated fats.
56
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 cisdouble
bonds to trans- double bonds.
D. T Animal fats have more saturated fats.
57
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
O
C
(CH2)14CH3
+3
H2O
H+
+3
CH2
OH
O
CH
OH
HO C
(CH2)14CH3
58
2. Saponification Value
Saponification - hydrolysis of ester under alkaline
condition.
O
H2 C O C R
O
HC O C R
O
H2 C O C R
H2 C OH
+
3 KOH
HC
OH
H2 C OH
+
O
3 R C OK
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.
60
Saponification
O
CH2 O C
(CH2)14CH3
O
O
CH O C
Na+ -O C
(CH2)14CH3 + 3NaOH
O
CH2 O C
(CH2)14CH3
CH2 OH
(CH2)14CH3
CH OH
+ 3
CH2 OH
“soap”
61
Saponification Value of Fats and Oils
Fat
Saponification #
Milk Fat
210-233
Coconut Oil
250-264
Cotton Seed Oil
189-198
Soybean Oil
189-195
Lard
190-202
2. Saponification Value Determination
Saponification # --mgs of KOH required to saponify 1 g of fat.
1. 5 g in 250 ml Erlenmeyer.
2. 50 ml KOH in Erlenmeyer.
3. Boil for saponification.
4. Titrate with HCl using phenolphthalein.
5. Conduct blank determination.
SP# =
56.1(B - S) x N of HCl
Gram of Sample
B - ml of HCl required by Blank.
S - ml of HCl required by Sample.
3. Iodine Number
Number of iodine (g) absorbed by 100 g of oil.
Molecular weight and iodine number can calculate
the number of double bonds. 1 g of fat adsorbed
1.5 g of iodine value = 150.
Iodine Value Determination
Iodine Value = (ml of Na2S2O3 volume for blank - ml of
Na2S2O3 volume for sample)  N of Na2S2O3  0.127g/meq 
100
Weight of Sample (g)
CH
CH
CH
Cl
+ ICl
Iodine chloride
Excess unreacted ICl
ICl
I2 +
+
KI
2 Na2 S2 O3
KCl
+
Na2 S4 O6
I2
+ 2 NaI
CH
I
Iodine Numbers of Triglycerides
Fatty Acids
# of Double-bonds
Iodine #
Palmitoleic Acid
1
95
Oleic Acid
1
86
Linoleic Acid
2
173
Linolenic Acid
3
261
Arachidonic Acid
4
320
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
67
Solution
What products are obtained from the
complete hydrolysis of glyceryl
trioleate?
1. Glycerol and 3 oleic acids
68
Learning Check
Write the product of the following
reaction.
O
CH2
CH
CH2
O
O
O
C
O
(CH2)5CH CH(CH2)7CH3
C (CH2)5CH
O
C
(CH2)5CH
CH(CH2)7CH3 + 3 H2
Ni
CH(CH2)7CH3
69
Solution
O
CH2
O
C (CH2)14CH3
O
CH
O
C (CH2)14CH3
O
CH2
O
C
(CH2)14CH3
70
Chapter 17
Lipids
17.5
Glycerophospholipids
Fatty acid
Glycerol
Fatty acid
PO4
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Amino
alcohol
71
PHOSPHOLIPID
Lecithin (phosphatidyl choline)
O
O
R
C
H2 C
O
O
C
R
CH
CH3
O
H2 C
O
P
O_
Phosphatidic Acid
O
CH2
CH 2
+
N CH 3
CH3
Choline
Glycerophospholipids
Glycerophospholipids are
• The most abundant lipids in cell
membranes.
• Composed of glycerol, two fatty acids,
phosphate and an amino alcohol.
Fatty acid
Fatty acid
Glycerol
PO4
Amino
alcohol
73
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−
Amino alcohols
serine
74
Structure and Polarity of A
Glycerophospholipid
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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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76
Lecithin
• Abundant in brain and nerve tissues
• Found in egg yolk, what germ, yeast
O
CH2 O C (CH2)14CH3
O
CH O
CH2
C
O
(CH2)14CH3
+
O P O CH2CH2N(CH3)3
-
O
choline, an amino alcohol
77
Chapter 17 Lipids
17.6
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.
fatty acid
• Have polar and nonpolar regions.
sphingosine
PO4
amino
alcohol
79
Sphingosine
Sphingosine is a long-chain unsaturated amino alcohol.
CH3−(CH2)12 −CH=CH−CH−OH
│
CH−NH2
│
CH2−OH
sphingosine
80
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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81
Glycosphingolipids
• Glycosphingolipi
ds contain
monosaccharide
s bonded to the
–OH of
sphingosine by a
glycosidic bond.
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82
Glycosphingolipids and Cerebrosides
Glycosphingolipids
• Are sphingolipids that contain
monosaccharides.
• Can be a cerebroside with
galactose.
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83
Steroid Nucleus
A steroid nucleus
consists of
• 3 cyclohexane rings.
• 1 cyclopentane ring.
• No fatty acids.
steroid nucleus
84
Chapter 17 Lipids
17.7
Steroids: Cholesterol, Bile Salts, and
Steroid Hormones
CH3
CH3
CH3
CH3
CH3
HO
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85
STEROLS
Male & female sex hormones
Bile acids
Vitamin D
Adrenal corticosteroids
21
H3C
18
Cholesterol
H3C
HO
22
CH3
20
12
19
17
11
13
H3C
14
10
1
9
2
8
3
6 7
4
5
16
15
CH3
Cholesterol
Cholesterol
• Is the most abundant steroid in the
body.
• Has methyl CH3- groups, alkyl chain,
and -OH attached to the steroid
CH3
nucleus.
CH3
CH3
CH3
HO
CH3
87
Cholesterol, an
important constituent of cell
membranes, has a rigid ring
system and a short branched
HO
hydrocarbon tail.
Cholesterol
Cholesterol is largely
hydrophobic.
But it has one polar group,
a hydroxyl, making it
amphipathic.
PDB 1N83
cholesterol
HO
Cholesterol
Cholesterol
in membrane
Cholesterol inserts into bilayer membranes with its
hydroxyl group oriented toward the aqueous phase &
its hydrophobic ring system adjacent to fatty acid
chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds
with polar phospholipid head groups.
Cholesterol in the Body
• Cellular membranes
• Myelin sheath, brain, and nerve tissue
• Bile salts
• Hormones
• Vitamin D
90
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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92
FAT SOLUBLE VITAMINS
Vitamin A:
H3 C
CH3
CH3
5
8
9
CH3
CH3
7
6
4
3
CH2 OH
2
1
CH3
H 3C
Vitamin D2:
H 3C
H
CH3
CH 3
H
CH 2
Vitamin E:
R1
R2
HO
R3
HO
CH3
CH
3
O
(CH2 CH2 CH2 CH2 )2 CH2 CH2CH2 CH(CH3 )2
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.
95
Bile Salts
glycine, an amino acid
cholic acid, a bile acid
CH3
OH
CH3
O
C
CH2
N
COO- Na+
Polar region
H
CH3
HO
Nonpolar region
OH
sodium glycocholate, a bile salt
96
Bile Salts
• Synthesized in the liver from cholesterol
• Stored in the gallbladder
• Secreted into small intestine
• Mix with fats to break them part
• Emsulsify fat particles
97
Sex Hormones
CH3 OH
CH3
O
CH3 OH
CH3
HO
t e st ost e r on e
e st r ad iol
98
Lipoproteins
Lipoproteins
• Combine lipids with proteins and
phospholipids.
• Are soluble in water because the surface
consists of polar lipids.
99
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Types of Lipoproteins
Lipoproteins
• Differ in density, composition, and function.
• Include low-density lipoprotein (LDLs) and
high-density
lipoprotein (HDLs).
TABLE 17.5
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100
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.
101
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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.
102
Adrenal Corticosteroids
103
Soxhlet Method.
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
105
Solution
A. cholesterol
2 steroid
B. glycerol, 2 fatty acids, phosphate, and choline
4 phospholipid
C. glyceryl tristearate 3 triacylglycerol
D. sphingosine, fatty acid, phosphate, and choline
5 sphingolipid
E. estradiol 2 steroid
F. bile salts 2 steroid
G. lipids in plasma membranes
4 phospholipid, 5 sphingolipid
.
106
Chapter 17 Lipids
17.8
Cell Membranes
107
Plasma Membranes
• Surround cells
• Lipid bilayer pf phospholipids
• Nonpolar hydrocarbon tails in center
• Polar (hydrophilic) sections on outside
• Some unsaturated fatty acids give flexibility
• Keep aqueous contents inside
• Allow certain biochemicals to pass through
108
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.
109
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.
110
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.
111
Transport Pathways Through Cell
Membranes
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112
Other Structures in Membranes
• Cholesterol molecules add strength
• Glycolipids on surface communicate with other cells
• Proteins embedded in bilayer move certain
substances (water, K+, Cl-, HCO3-) across the cell
membrane
• Proteins on surface act as receptors for hormones
and other biochemicals
113
Diagram of a Plasma Membrane
Polar sections
Nonpolar tails
114
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
115
Solution
The transport of particles across a cell
membrane from
high concentration to low concentration is called
2. Diffusion
116