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25
Answers and Solutions to Text Problems
25.1
The bile salts emulsify fat to give small fat globules for lipase hydrolysis.
25.2
The triacylglycerols in the intestinal lining are coated with proteins to form lipoproteins called
chylomicrons, which are polar and can be transported through the lymph system and into the
bloodstream.
25.3
Fats are mobilized when blood glucose and glycogen stores are depleted.
25.4
Glycerol is phosphorylated using ATP to give glycerol-3-phosphate, which is oxidized to
dihydroxyacetone phosphate. This product can now enter glycolysis or gluconeogenesis.
25.5
Glycerol is converted to glycerol-3-phosphate and then to dihydroxyacetone phosphate, which is
an intermediate of glycolysis.
25.6
Glycerol is converted to glycerol-3-phosphate and then to dihydroxyacetone phosphate, which
can enter gluconeogenesis to produce glucose.
25.7
Fatty acids are activated in the cytosol of the mitochondria.
25.8
Carnitine is a charged carrier that transports fatty acids across the inner mitochondrial into the
matrix.
25.9
The coenzymes FAD and NAD+ are required for _-oxidation.
25.10
Isomerization occurs in _ oxidation when the fatty acid has an unsaturated site. The typical cis
double bond must be converted to a trans double bond for the hydration step of beta oxidation.
25.11
The designation beta (_) carbon is based on the common names of carboxylic acids whereby the
alpha _ carbon and the beta (_) carbons are adjacent to the carboxyl group.
O
_
||
a. CH3CH2CH2CH2CH2CH2CH2CSCoA
O
_
||
b. CH3(CH2)14CH2CH2CSCoA
O
_
||
c. CH3CH2CH=CHCH2CH2CH2CH2CH2CSCoA
25.12
OH
O
|
||
a. CH3(CH2)12CHCH2CSCoA
H
O
|
||
b. CH3(CH2)6C=CCSCoA
|
H
Metabolic Pathways for Lipids and Amino Acids
O
||
c. CH3(CH2)4CSCoA
25.13
O
||
+ CH3CSCoA
O
||
a., b. CH3(CH2)6CH2CH2CSCoA
_
_
c.
O
||
CH3(CH2)8CSCoA + NAD+ + FAD + H2O + SHCoA →
O
O
||
||
CH3(CH2)6CSCoA + CH3CSCoA + NADH + H+ + FADH2
d. CH3(CH2)8COOH + 5CoA + 4FAD + 4NAD+ + 4H2O →
5Acetyl CoA + 4FADH2 + 4NADH + 4H+
25.14
O
||
a., b. CH3(CH2)18CH2CH2CSCoA
_
_
c.
O
||
CH3(CH2)18CSCoA + NAD+ + FAD + H2O + SHCoA →
O
O
||
||
CH3(CH2)16CSCoA + CH3CSCoA + NADH + H+ + FADH2
d. CH3(CH2)18COOH + 10 CoA + 9FAD + 9NAD+ + 9H2O →
10Acetyl CoA + 9FADH2 + 9NADH + 9H+
25.15
The hydrolysis of ATP to AMP hydrolyzes ATP to ADP, and ADP to AMP, which provides the
same amount of energy as the hydrolysis of 2 ATP to 2 ADP.
25.16
12 ATP are obtained when one acetyl CoA goes through the citric acid cycle
25.17
a. The _-oxidation of a chain of 10 carbon atoms produces 5 acetyl CoA units.
b. A C10 fatty acid will go through 4 _-oxidation cycles.
c. 60 ATP from 5 acetyl CoA (citric acid cycle) + 12 ATP from 4 NADH + 8 ATP from 4
FADH2 –2 ATP (activation) = 80 –2 = 78 ATP
25.18
a. 10 acetyl CoA units
25.19
Ketogenesis is the synthesis of ketone bodies from excess acetyl CoA from fatty acid oxidation,
which occurs when glucose is not available for energy. This occurs in starvation, fasting, and
diabetes.
25.20
Without carbohydrates, the body breaks down body fat, which results in the production of many
acetyl CoA molecules.
25.21
Acetoacetate undergoes reduction using NADH + H+ to yield _-hydroxybutyrate.
b. 9 cycles
c. 163 ATPs
Chapter 25 Answers and Solutions
25.22
Acetoacetate undergoes decarboxylation to form acetone.
25.23
High levels of ketone bodies lead to ketosis, a condition characterized by acidosis (a drop in
blood pH values), and characterized by excessive urination and strong thirst.
Diabetics are unable to metabolize glucose and break down large amount of fats, which give
high levels of acetyl CoA resulting in the formation of ketone bodies.
25.24
25.25
Fatty acid synthesis takes place in the cytosol of cells in liver and adipose tissue.
25.26
25.27
ACP, which is an acyl carrier protein, is used to activate acetyl and acyl groups.
Fatty acid synthesis starts when acetyl CoA, HCO3 , and ATP produce malonyl CoA.
25.28
In fatty acid synthesis, malonyl-ACP adds another acetyl group to a growing acyl-ACP chain.
25.29
a. (3) malonyl CoA transacylase converts malonyl CoA to malonyl ACP.
b. (1) acetyl CoA carboxylase combines acetyl CoA with bicarbonate to yield malonyl CoA.
c. (2) acetyl CoA transacylase converts acetyl CoA to acetyl ACP.
25.30
a. (3) 3-hydroxy-ACP dehydrase
c. (1) _-ketoacyl-ACP synthase
25.31
25.32
b. (4) enoyl-ACP reductase
d. (2) _-ketoacyl-ACP reductase
a. A C10 fatty acid requires the formation of 4 malonyl ACP, which uses 4 HCO3 .
b. 4 ATP are required to produce 4 malonyl CoA.
c. 5 acetyl CoA are needed to make 1 acetyl ACP and 4 malonyl ACP.
d. A C10 fatty acid requires 4 malonyl ACP and 1 acetyl ACP.
e. A C10 fatty acid chain requires 4 cycles with 2 NADPH/cycle or a total of 8 NADPH.
f. The four cycles remove a total of 4 CO2.
a. A C14 fatty acid requires the formation of 6 malonyl ACP, which requires 6HCO3 .
b. 6 ATP are required to produce 6 malonyl CoA.
c. 7 acetyl CoA are needed to make 1 acetyl ACP and 6 malonyl ACP.
d. A C14 fatty acid requires 6 malonyl ACP and 1 acetyl ACP.
e. A C14 fatty acid chain requires 6 cycles with 2 NADPH/cycle or a total of 12 NADPH.
f. The six cycles remove a total of 6 CO2.
25.33
The digestion of proteins begins in the stomach and is completed in the small intestine.
25.34
Protein turnover is the process of synthesizing proteins and breaking them down.
25.35
Nitrogen-containing compounds in the cells include hormones, heme, purines and pyrimidines
for nucleotides, proteins, nonessential amino acids, amino alcohols, and neurotransmitters.
25.36
If they are not used to build protein, amino acids are excreted because they cannot be stored.
25.37
The reactants are an amino acid and an _-keto acid, and the products are a new amino acid and a
new _-keto acid.
25.38
transaminases (aminotransferases)
Metabolic Pathways for Lipids and Amino Acids
25.39
In transamination, an amino group replaces a keto group in the corresponding _-keto acid.
O
O
CH3 O
||
||
|
||
b. CH3CCOO¯ c. CH3CHCCOO¯
a. HCCOO¯
25.40
O
||
a. OOCCH2CCOO
b.
CH3 O
|
||
CH3CH2CHCCOO¯
O
||
c. HOCH2CCOO¯
25.41
In an oxidative deamination, the amino group in an amino acid such as glutamate is removed as
an ammonium ion. The reaction requires NAD+ or NADP+.
+
Glutamate
NH3
|
dehydrogenase
¯
OOCCHCH2CH2COO¯ + H2O + NAD+ (NADP+) →
Glutamate
O
||
¯
OOCCCH2CH2COO¯ + NH4+ + NADH (NADPH) + H+
_-Ketoglutarate
25.42
Glutamate forms when the amino group from any of the amino acids is transferred to
_-ketoglutarate. In the process of oxidation deamination, glutamate converts that amino group to
ammonium ion.
25.43
NH4+ is toxic if allowed to accumulate in the liver.
25.44
Urea formation requires two ATP.
25.45
O
||
H2NCNH2
25.46
O
O
||
||
H2NCOPO|
O-
25.47
The carbon atom in urea is obtained from the CO2 produced by the citric acid cycle.
25.48
One ATP is used in each turn of the urea cycle.
Chapter 25 Answers and Solutions
25.49
Glucogenic amino acids can be used to produce intermediates for glucogenesis, which is glucose
synthesis.
25.50
A ketogenic amino acid generates acetoacetyl CoA or acetyl CoA, which can enter the
ketogenesis pathway and form ketone bodies or lipogenesis and form fatty acids.
25.51
a.
b.
c.
d.
25.52
a. Acetoacetyl CoA; acetyl CoA
c. pyruvate
25.53
Humans can synthesize only nonessential amino acids.
25.54
The essential amino acids must be obtained from the diet.
25.55
Glutamine synthetase catalyzes the addition of an amino group to glutamate using energy from
the hydrolysis of ATP.
25.56
The synthesis of tyrosine requires phenylalanine.
25.57
Phenylketonurnia
25.58
PKU is treated with a diet that is low in phenylalanine and high in tyrosine.
25.59
Triacylglycerols are hydrolyzed to monoacylglycerols and fatty acids in the small intestine,
which are reformed into triacylglycerols in the intestinal lining for transport as lipoproteins to the
tissues.
25.60
Chylomicrons are lipoproteins in which triacylglycerols are coated with proteins.
25.61
Fats can be stored in unlimited amounts in adipose tissue compared to the limited storage of
carbohydrates as glycogen.
25.62
Stored fats are mobilized when triacylglycerols in the adipose tissue are converted to fatty acids
and glycerol.
25.63
The fatty acids cannot diffuse across the blood-brain barrier.
25.64
Red blood cells do not have mitochondria, which are required for the oxidation of fatty acids.
25.65
a. Glycerol is converted to glycerol- 3-phosphate and to dihydroxyacetone phosphate, which
can enter glycolysis or gluconeogenesis.
b. Activation of fatty acids occurs on the outer mitochondrial membrane.
c. The energy cost is equal to 2 ATP.
d. Only fatty acyl CoA can move into the intermembrane space for transport by carnitine into
the matrix.
25.66
a.
b.
c.
d.
The three-carbon atom structure of alanine is converted to pyruvate.
The four-carbon structure of aspartate is converted to fumarate or oxaloacetate.
Valine is converted to succinyl CoA.
The five-carbon structure from glutamine can be converted to _-ketoglutarate.
b. oxaloacetate
d. _-ketoglutarate
Activation of a fatty acid involves the reaction of ATP and coenzyme A.
The oxidation of a fatty acid occurs at the _ carbon.
Reaction 1 requires FAD and reaction 3 requires NAD+.
One cycle produces 5 ATP
Metabolic Pathways for Lipids and Amino Acids
25.67
Lauric acid, CH3(CH2)10COOH, is a C12 fatty acid. (C12H24O2)
O
||
a. and b. CH3(CH2)8CH2CH2 CCoA
_
_
c. Lauryl-CoA + 5 CoA + 5 FAD + 5 NAD+ + 5 H2O →
6 Acetyl CoA + 5 FADH2 + 5 NADH + 5H+
d. Six acetyl CoA units are produced.
e. Five cycles of _ oxidation are needed.
f.
activation
→ -2 ATP
6 acetyl CoA ✕ 12
→ 72 ATP
5 FADH2
✕ 2
→ 10 ATP
5 NADH
✕ 3
→ 15ATP
Total
95 ATP
25.68
Caproic acid with 6 carbon atoms will produce 3 acetyl CoA and go through the _ oxidation cycle
two times.
activation
→ -2 ATP
3 acetyl CoA ✕ 12
→ 36 ATP
2 FADH2
✕ 2
→
4 ATP
2 NADH
✕ 3
→
6 ATP
Total
44 ATP
When glucose undergoes complete oxidation, a total of 36 ATP are produced.
25.69
a. _ oxidation
c. Fatty acid synthesis
e. Fatty acid synthesis
b. _ oxidation
d. _ oxidation
f. Fatty acid synthesis
25.70
a. fatty acid synthesis
c. _ oxidation
e. _ oxidation
b. _ oxidation
d. _ oxidation
f. _ oxidation
25.71
a. (1) fatty acid oxidation
b. (2) the synthesis of fatty acids
25.72
a. (2) the synthesis of fatty acids
b. (1) _ oxidation
25.73
Ammonium ion is toxic if allowed to accumulate in the liver.
25.74
Ornithine is regenerated.
25.75
a. Citrulline
25.76
a. Urea and aspartate are produced from arginine.
b. Arginine and fumarate are produced from argininosuccinate.
25.77
a.
b.
c.
d.
25.78
a. acetyl CoA, acetoacetyl CoA
c. pyruvate
b. Carbamoyl phosphate
The carbon atom structure of valine is converted to pyruvate.
Lysine, a ketogenic amino acid, is converted to acetoacetyl CoA.
The degradation of methionine produces succinyl-CoA.
Glutamate can be converted to five-carbon _-ketoglutarate.
b. acetyl CoA
d. fumarate, acetoacetyl CoA
Chapter 25 Answers and Solutions
25.79
Serine is degraded to pyruvate, which is oxidized to acetyl CoA. The oxidation produces NADH
+ H+, which provides 3 ATP. In one turn of the citric acid cycle, the acetyl CoA provides 12
ATP. Thus, serine can provide a total of 15 ATP.
25.80
14 kg fat ✕ 1000 g/kg ✕0.49 moles ATP/g fat = 6900 moles ATP