Download Chapter 15 Lipids Lipids Types of Lipids Classes of Lipids Fatty

Chapter 15
Lipids
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.
15.1 Lipids
15.2 Fatty Acids
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Types of Lipids
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Classes of Lipids
The types of lipids containing fatty acids are
• waxes
• fats and oils (triacylglycerols)
• glycerophospholipids
• prostaglandins
The types of lipids that do not contain fatty acids are
• steroids
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Saturated and Unsaturated Fatty
Acids
Fatty Acids
Fatty acids are
• long-chain carboxylic acids.
• typically 12-18 carbon atoms.
• insoluble in water.
• saturated or unsaturated.
Fatty acids are
• saturated with
all single C–C
bonds.
• unsaturated
with one or
more double
C=C bonds.
Olive oil contains 84%
unsaturated fatty acids and
16% saturated fatty acids.
O
C OH
palmitic acid, a saturated acid
O
C OH
palmitoleic acid, an unsaturated acid
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Properties of Unsaturated Fatty
Acids
Properties of Saturated Fatty Acids
Unsaturated fatty acids
• contain one or more cis double C=C
bonds.
• 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.
Saturated fatty acids
• contain only single C–C bonds.
• are closely packed.
• have strong attractions between chains.
• have high melting points.
• are solids at room temperature.
HOOC
H
COOH
H C C
“kinks” in
chain
H
COOH
COOH
COOH
C
C
H
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Melting Points of Some Saturated
Fatty Acids
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Melting Points of Some
Unsaturated Fatty Acids
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Learning Check
Solution
Assign the melting points of –17 °C, 13 °C, and 69 °C
to the correct fatty acid. Explain.
stearic acid (18 C)
oleic acid
(18 C)
linoleic acid (18 C)
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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
saturated
one double bond
two double bonds
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Chapter 15
Lipids
Waxes
Waxes are
• esters of saturated fatty acids and long-chain alcohols.
• coatings that prevent loss of water by leaves of plants.
15.3
Waxes, Fats, and Oils
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Fats and Oils: Triacylglycerols
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Triacylglycerols
In a triacylglycerol, glycerol forms ester bonds with
three fatty acids.
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.
Ester Bonds
Copyright © 2009 by Pearson Education, Inc.
Copyright © 2009 by Pearson Education, Inc.
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Formation of a Triacylglycerol
Glycerol
CH2
+
OH
CH
OH
CH2
OH
+
three fatty acids
HO C
O
(CH2)14CH3
HO C
O
(CH2)14CH3
HO C
(CH2)14CH3
Learning Check
What are the fatty acids in the following triacylglycerol?
triacylglycerol
O
16
O
CH2
O
CH2 O C
(CH2)14CH3
CH
(CH2)14CH3 + 3H O
2
CH2
O
O
CH O C
C
(CH2)16CH3
O
O
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
O
CH2 O C
(CH2)14CH3
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Solution
Melting Points of Fats and Oils
O
CH2
O
CH
O
CH2
O
C
(CH2)16CH3
A fat
• is usually solid at room temperature.
• is prevalent in meats, whole milk, butter, and cheese.
An oil
• is usually liquid at room temperature.
• is prevalent in plants such as olive and safflower.
Stearic acid
O
C (CH2)7CH CH(CH2)7CH3
O
C
(CH2)12CH3
Oleic acid
Myristic acid
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Diagram of Triacylglycerol with
Unsaturated Fatty Acids
Oils with Unsaturated Fatty Acids
Oils
• have more unsaturated fats.
• have cis double bonds that cause “kinks” in the fatty
acid chains.
• with “kinks” in the chains do not allow the
triacylglycerol molecules to pack closely.
• have lower melting points than saturated fatty acids.
• are liquids at room temperature.
Unsaturated
fatty acid
chains with
kinks cannot
pack closely.
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Percent Saturated and Unsaturated
Fatty Acids In Fats and Oils
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Chapter 15
Lipids
15.4
Chemical Properties of Triacylglycerols
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Chemical Properties of
Triacylglycerols
Hydrogenation of Oils
The chemical reactions of triacylglycerols are similar
to those of alkenes and esters.
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.
• 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.
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Hydrogenation
Learning Check
What products are obtained from the complete
hydrogenation of glyceryl trioleate?
O
CH2
O
C
Ni
(CH2)5CH CH(CH2)7CH3
+ 3H2
O
CH
O
CH2
O
C (CH2)5CH CH(CH2)7CH3
CH2
O
C
(CH2)5CH CH(CH2)7CH3
Glyceryl tripalmitoleate
(tripalmitolean)
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O
O
C
(CH2)14CH3
O
CH
O
CH2
O
C (CH2)14CH3
O
C
1. Glycerol and 3 oleic acids
2. Glyceryltristearate
3. Glycerol and 3 stearic acids
(CH2)14CH3
Glyceryl tripalmitate
(tripalmitin)
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OlestraTM, a Fat Substitute
Solution
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.
What products are obtained from the complete
hydrogenation of glyceryl trioleate?
2. Glyceryltristearate
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Hydrogenation and Trans Fatty
Acids
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
Most naturally occurring fatty acids have cis double
bonds.
• During hydrogenation, some cis double bonds are converted to
trans double bonds.
C=C
H
• In the body, trans fatty acids behave like saturated fatty acids.
H
• It is estimated that 2-4% of our total Calories is in the form of
trans fatty acid.
• trans have bulky groups on opposite sides of C=C.
H
CH3─ (CH2)5
C=C
H
(CH2)7─ COOH
• Several studies reported that trans fatty acids raise LDLcholesterol and lower HDL-cholesterol.
trans
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Hydrogenation of Unsaturated
Fats
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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.
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Solution
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Hydrolysis
In hydrolysis,
• triacylglycerols split into glycerol and three fatty acids.
• an acid or enzyme catalyst is required.
(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.
O
CH2
O
C
O
CH
O
C (CH2)14CH3 + H2O
O
CH2
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O
C
(CH2)14CH3
(CH2)14CH3
H+
CH2
OH
CH
OH
CH2
OH
O
+
HO C
(CH2)14CH3
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Saponification and Soap
Saponification
O
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.
CH2 O C
(CH2)14CH3
O
CH O C
(CH2)14CH3
+ 3NaOH
O
CH2 O C
CH2 OH
(CH2)14CH3
CH OH
O
+ 3Na+ -O C (CH2)14CH3
“soap”
CH2 OH
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Learning Check
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Solution
What products are obtained from the complete
hydrolysis of glyceryl trioleate?
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
1. Glycerol and 3 oleic acids
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Learning Check
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Solution
Write the product of the following reaction:
O
O
CH2 O C
O
CH2
O
C (CH2)14CH3
O
CH
O
C (CH2)14CH3
O
(CH2)5CH CH(CH2)7CH3
CH
O
C (CH2)5CH CH(CH2)7CH3 + 3H2
O
CH2
O
C
(CH2)5CH
Ni
CH2
CH(CH2)7CH3
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O
C
(CH2)14CH3
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Chapter 15
Lipids
Glycerophospholipids
15.5
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
Fatty acid
Glycerol
Glycerol
PO4
Fatty acid
Amino
alcohol
PO4
Amino
alcohol
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Structure and Polarity of a
Glycerophospholipid
Polarity of Glycerophospholipids
A glycerophospholipid has
• two nonpolar fatty acid chains.
• a phosphate group and a polar amino alcohol.
CH3
│+
HO−CH2−CH2−N−CH3
│
Choline
CH3
+
HO−CH2−CH2−NH3
Ethanolamine
+
NH3
│
HO−CH2−CH−COO− Serine
Amino alcohols
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Lecithin and Cephalin
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Learning Check
Identify each as
A. fatty acid
C. amino alcohol
Lecithin and cephalin are glycerophospholipids
• abundant in brain and nerve tissues.
• found in egg yolk, wheat germ, and yeast.
B. triacylglycerol
D. glycerophospholipid
1. glyceryl trioleate
2. cephalin
3. choline
4. palmitic acid
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Solution
Identify each as
A. fatty acid
C. amino alcohol
1. glyceryl trioleate
2. cephalin
3. choline
4. palmitic acid
Chapter 15
Lipids
15.6
Steroids: Cholesterol and Steroid
Hormones
B. triacylglycerol
D. glycerophospholipid
B. triacylglycerol
D. Glycerophospholipid
C. amino alcohol
A. fatty acid
CH3
CH3
CH3
CH3
CH3
HO
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Steroid Nucleus
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Cholesterol
Cholesterol
• is the most abundant steroid in the body.
• has methyl CH3- groups, alkyl chain, and -OH
attached to the steroid nucleus.
A steroid nucleus
consists of
• 3 cyclohexane rings.
• 1 cyclopentane ring.
• no fatty acids.
CH3
CH3
CH3
CH3
CH3
steroid nucleus
HO
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Cholesterol in the Body
Cholesterol
• 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.
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Cholesterol in Foods
A normal, open artery.
An artery clogged
by cholesterol
plaque
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Cholesterol
• is considered
elevated if
plasma
cholesterol
exceeds 200
mg/dL.
• is synthesized in
the liver and
obtained from
foods.
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Learning Check
Solution
Match the components of the cholesterol molecule with
the following:
___ carbon chain
___hydroxyl group
___ steroid nucleus
___methyl group
CH3
CH3
Match the components of the cholesterol molecule with
the following:
_D carbon chain
_A_hydroxyl group
_C steroid nucleus
_B_methyl group
D
CH3
CH3
CH3
CH3
B
CH3
CH3
CH3
B
CH3
A
D
A
HO
C
HO
C
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Lipoproteins
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Types of Lipoproteins
Lipoproteins
• differ in density, composition, and function.
• include low-density lipoproteins (LDLs) and highdensity lipoproteins (HDLs).
Lipoproteins
• combine lipids
with proteins
and
phospholipids.
• are soluble in
water because
the surface
consists of
polar lipids.
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Transport of Lipoproteins in the
Body
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Steroid Hormones
Steroid hormones are
• chemical messengers in cells.
• sex hormones.
- androgens in males (testosterone)
- estrogens in females (estradiol)
• Adrenocortical hormones from adrenal glands.
- mineralocorticoids (electrolyte balance)
- glucocorticoids (regulate glucose level)
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Steroid Hormones
Adrenal Corticosteroids
Steroid hormones
• are produced from
cholesterol.
Steroid hormones called adrenal corticosteroids
• 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.
• include sex
hormones such as
androgens
(testosterone) in
males and estrogens
(estradiol) in
females.
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Anabolic Steroids
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Adrenal Corticosteroids
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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Learning Check
Solution
Identify each lipid as a
(1) fatty acid, (2) steroid, or (3) triacylglycerol.
A.
B.
C.
D.
E.
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Identify each lipid as a
(1) fatty acid, (2) steroid, or (3) triacylglycerol.
A. 2 cholesterol
B. 1 stearic acid
C. 3 glyceryl tristearate
D. 2 estradiol
E. 2 contains no fatty acids
cholesterol
stearic acid
glyceryl tristearate
estradiol
contains no fatty acids
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Chapter 15
Lipids
Cell Membranes
15.7
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.
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Fluid Mosaic Model of Cell
Membranes
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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.
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Transport Pathways Through Cell
Membranes
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.
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Learning Check
Solution
The transport of particles across a cell membrane from
The transport of particles across a cell membrane from
high concentration to low concentration is called
high concentration to low concentration is called
2. diffusion.
1. facilitated transport.
2. diffusion.
3. active transport.
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