1. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.1
Digestion of Triacylglycerols
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2. Digestion of Fats (Triacylglycerols)
In the digestion of fats (triacylglycerols),
Bile salts break fat globules into smaller particles called micelles in the small intestine.
Pancreatic lipases hydrolyze ester bonds to form monoacylglycerols and fatty acids, which recombine in the intestinal lining.
Fatty acids bind with proteins forming lipoproteins to transport triacylglycerols to the cells of the heart, muscle, and adipose tissues.

3. Digestion of Triacylglycerols
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4. Fat Mobilization Fat mobilization
Breaks down triacylglycerols in adipose tissue.
Forms fatty acids and glycerol.
Hydrolyzes fatty acid initially from C1 or C3 of the fat.
triacylglycerols + 3 H2O
glycerol + 3 fatty acids
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5. Metabolism of Glycerol
Glycerol from fat digestion
Adds a phosphate from ATP to form glycerol-3-phosphate.
Undergoes oxidation of the –OH group to dihydroxyacetone phosphate.
Becomes an intermediate used in glycolysis and gluconeogenesis.
Glycerol + ATP + NAD+
dihydroxyacetone phosphate + ADP + NADH + H+

6. Oxidation of Glycerol

7. Learning Check Give answers for the following questions on fat
digestion.
1. What is the function of bile salts in fat digestion?
2. Why are the triacylglycerols in the intestinal lining
coated with proteins to form chylomicrons?
3. How is glycerol utilized?

8. Solution 1. What is the function of bile salts in fat digestion?
Bile salts break down fat globules allowing
pancreatic lipases to hydrolyze the triacylglycerol.
2. Why are the triacylglycerols in the intestinal lining coated with proteins to form chylomicrons?
The proteins coat the triacylglycerols to make water­
soluble chylomicrons that move into the lymph and
bloodstream.
3. How is glycerol utilized?
Glycerol adds a phosphate and is oxidized to an
intermediate of the glycolysis and gluconeogenesis
pathways.

9. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.2
Oxidation of Fatty acids
24.3
ATP and Fatty Acid Oxidation
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10. Fatty Acid Activation Fatty acid activation
Allows the fatty acids in the cytosol to enter the mitochondria for oxidation.
Combines a fatty acid with CoA to yield fatty acyl CoA that combines with carnitine.
Fatty acyl
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11. Transport of Fatty Acyl CoA
Fatty acyl-CoA forms fatty acyl-carnitine that transports the fatty acyl group into the matrix.
The fatty acyl group recombines with CoA for oxidation.
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12. Summary of Fatty Acid Activation
Fatty acid activation is complex, but it regulates the degradation and synthesis of fatty acids.
Fatty acyl
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13. Beta-Oxidation of Fatty Acids
Fatty acyl CoA undergoes
β oxidation in a cycle of four
reactions.
In reaction 1, oxidation
Removes H atoms from the  and  carbons.
Forms a trans C=C bond.
Reduces FAD to FADH2.
 
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14. Beta-Oxidation of Fatty Acids
In reaction 2 of
β oxidation, hydration
Adds water across the trans C=C bond.
Forms a hydroxyl group (—OH) on the  carbon.
 
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15. Beta-Oxidation of Fatty Acids
In reaction 3 of β
oxidation, a second
oxidation
Oxidizes the hydroxyl group.
Forms a keto group on the  carbon.
 
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16. Beta()-Oxidation of Fatty Acids
In Reaction 4 of β-
oxidation, acetyl CoA
is cleaved
By splitting the bond between the  and  carbons.
To form a shortened fatty acyl CoA that repeats steps of -oxidation.
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17. Learning Check Match the reactions of -oxidation with each:
1) oxidation 1 2) hydration
3) oxidation 2 4) acetyl CoA cleaved
A. Water is added.
B. FADH2 forms.
C. A two-carbon unit is removed.
D. A hydroxyl group is oxidized.
E. NADH forms.

18. Solution Match the reactions of -oxidation with each:
1) oxidation 1 2) hydration
3) oxidation 2 4) acetyl CoA cleaved
A Water is added.
B FADH2 forms.
C A two-carbon unit is removed.
D A hydroxyl group is oxidized.
E NADH forms.

19. Beta()-Oxidation of Myristic (C14) Acid
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20. Beta()-Oxidation of Myristic (C14) Acid (continued)
7 Acetyl CoA 6
cycles

21. Fatty Acid Length and -Oxidation
The length of a fatty acid
Determines the number of oxidations
Determines the total number of acetyl CoA groups.
Carbons in Acetyl CoA -Oxidation Cycles
Fatty Acid (#C/2) (#C/2 –1)

22. Learning Check
A. The number of acetyl CoA groups produced by the complete -oxidation of palmitic acid (C16 ):
1) ) 8 3) 7
B. The number of oxidation cycles to completely oxidize palmitic acid (C16 ):

23. Solution
A. The number of acetyl CoA groups produced by the complete -oxidation of palmitic acid (C16 ):
2) (16 C/2 = 8)
B. The number of oxidation cycles to completely oxidize palmitic acid (C16 ):
3) 7 (16 C/ = 7)

24. ATP and -Oxidation Activation of a fatty acid requires 2 ATP
One cycle of oxidation of a fatty acid produces
1 NADH ATP
1 FADH ATP
Acetyl CoA entering the citric acid cycle produces
1 Acetyl CoA 12 ATP

25. ATP for Lauric Acid C12 ATP production for lauric acid (12 carbons):
Activation of lauric acid ATP
6 Acetyl CoA
6 acetyl CoA x 12 ATP/acetyl CoA 72 ATP
5 Oxidation cycles
5 NADH x 3ATP/NADH 15 ATP
5 FADH2 x 2ATP/FADH2 10 ATP
Total 95 ATP

26. Learning Check 1) 108 ATP 2) 146 ATP 3) 148 ATP
The total ATP produced from the -oxidation of stearic acid (C18) is
1) 108 ATP
2) 146 ATP
3) 148 ATP

27. Solution 2) 146 ATP Activation -2 ATP 9 Acetyl CoA x 12 ATP 108 ATP
The total ATP produced from the -oxidation of stearic acid (C18) is:
2) 146 ATP
Activation ATP
9 Acetyl CoA x 12 ATP 108 ATP
8 NADH x 3 ATP 24 ATP
8 FADH2 x 2 ATP 16 ATP
146 ATP

28. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.4
Ketogenesis and Ketone Bodies
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29. Ketone Bodies If carbohydrates are not available
Body fat breaks down to meet energy needs.
Keto compounds called ketone bodies form.
Ketone bodies
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30. Ketogenesis In ketogenesis Large amounts of acetyl CoA accumulate.
Two acetyl CoA molecules combine to form acetoacetyl CoA.
Acetoacetyl CoA hydrolyzes to acetoacetate, a ketone body.
Acetoacetate reduces to -hydroxybutyrate or loses CO2 to form acetone, both ketone bodies.

31. Reactions of Ketogenesis
Ketone bodies
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32. Ketosis Ketosis occurs In diabetes, diets high in fat, and starvation.
As ketone bodies accumulate.
When acidic ketone bodies lowers blood pH below 7.4 (acidosis).
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33. Ketone Bodies and Diabetes
In diabetes
Insulin does not function property.
Glucose levels are insufficient for energy needs.
Fats are broken down to acetyl CoA.
Ketogenesis produces ketone bodies.
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34. Learning Check In ketogenesis, match the type of reaction with
1) oxidation 2) reduction 3) decarboxylation
A. acetoacetate produces acetone
B. acetoacetate produces β-hydroxybutyrate

35. Solution In ketogenesis, match the type of reaction with
1) oxidation 2) reduction 3) decarboxylation
A. acetoacetate produces acetone
B. acetoacetate produces β-hydroxybutyrate 2

36. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.5
Fatty Acid Synthesis
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37. Lipogenesis: Fatty Acid Synthesis
Is the synthesis of fatty acids from acetyl CoA.
Occurs in the cytosol.
Uses reduced coenzyme NADPH (NADH with a phosphate group).
Requires an acyl carrier protein (ACP).
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38. Synthesis of Malonyl CoA
For fatty acid synthesis,
Acetyl CoA combines with bicarbonate to form malonyl CoA.
ATP hydrolysis provides energy.
O acetyl CoA
|| carboxylase
CH3—C—S—CoA + HCO3- + ATP
acetyl CoA
O O
|| ||
-O—C—CH2—C—S—CoA + ADP + Pi + H+
malonyl CoA

39. Acetyl and Malonyl Acyl Carrier Proteins (ACP)
Active forms of acetyl ACP and malonyl-ACP are
produced by combining with acyl carrier proteins (ACP).
O O
║ ║
CH3—C—S—CoA + HS-ACP CH3—C—S—ACP + HS-CoA
acetyl-ACP
O O
|| ||
-O—C—CH2—C—S—CoA + HS-ACP
-O—C—CH2—C—S—ACP + HS-CoA
malonyl-ACP

40. Fatty Acid Synthesis: Condensation and Reduction
In reactions 1 and 2 of fatty
acid synthesis
Condensation (1) by a synthase combines acetyl-ACP with malonyl-ACP to form acetoacetyl-ACP (4C) and CO2.
Reduction(2) converts a ketone to an alcohol using NADPH.
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41. Fatty Acid Synthesis: Dehydration and Reduction
In reactions 3 and 4 of
fatty acid synthesis
Dehydration(3) forms a trans double bond.
Reduction (4) converts the double bond to a single bond using NADPH.
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42. Fatty Acid Synthesis (Lipogenesis) Cycle Repeats
continues as
Malonyl-ACP combines with the four-carbon butyryl-ACP to form a six-carbon-ACP.
The carbon chain lengthens by two carbons each cycle.
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43. Fatty Acid Synthesis (Lipogenesis) Cycle Completed
Is completed when palmitoyl ACP reacts with water to give palmitate (C16) and free ACP.
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44. Summary of Lipogenesis
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45. Fatty Acid Length In fatty acid synthesis
Shorter fatty acids undergo fewer cycles.
Longer fatty acids are produced from palmitate using special enzymes.
Unsaturated cis bonds are incorporated into a 10-carbon fatty acid that is elongated further.

46. Regulation of Fatty Acid Synthesis
In fatty acid synthesis
A high level of blood glucose and insulin stimulates glycolysis and pyruvate oxidation.
More acetyl CoA is available to form fatty acids.

47. Comparing -Oxidation and Fatty Acid Synthesis
TABLE 24.1
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48. Learning Check Match each with the description below:
1) mitochondria 2) cytosol
3) glucagon 4) insulin
5) acetyl ACP 6) malonyl ACP
A. Site of fatty acid synthesis.
B. Site of -oxidation.
C. Starting material for lipogenesis.
D. Compound added to elongate acyl-ACP.
E. Activates -oxidation.
F. Activates lipogenesis.

49. Solution Match each with the description below:
1) mitochondria 2) cytosol
3) glucagon 4) insulin
5) acetyl ACP 6) malonyl ACP
A Site of fatty acid synthesis.
B Site of -oxidation.
C. 5,6 Starting material for lipogenesis.
D. 6 Compound added to elongate acyl-ACP.
E. 3 Activates -oxidation.
F. 4 Activates lipogenesis.

50. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.6
Digestion of Proteins
24.7
Degradation of Amino Acids
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51. Digestion of Proteins The digestion of proteins (stage 1)
Begins in the stomach where HCl in stomach acid activates pepsin to hydrolyze peptide bonds.
Continues in the small intestine where trypsin and chymotrypsin hydrolyze peptides to amino acids.
Is complete as amino acids enter the bloodstream for transport to cells.

52. Digestion of Proteins Copyright © 2007 by Pearson Education, Inc.
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53. Learning Check Match the end products of digestion with the types of
food:
1. amino acids 2. fatty acids and glycerol
3. glucose
A. fats
B. proteins
C. carbohydrates

54. Solution Match the end products of digestion with the types of food:
1. amino acids 2. fatty acids and glycerol
3. glucose
A. fats 2. fatty acids and glycerol
B. proteins amino acids
C. carbohydrates 3. glucose

55. Proteins in the Body Proteins provide
Amino acids for protein synthesis.
Nitrogen atoms for nitrogen-containing compounds.
Energy when carbohydrate and lipid resources are not available.
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56. Transamination In transamination
Amino acids are degraded in the liver.
An amino group is transferred from an amino acid to an -keto acid, usually -ketoglutarate.
The reaction is catalyzed by a transaminase or aminotransferase.
A new amino acid, usually glutamate, and a new -keto acid are formed.

57. A Transamination Reaction
NH3+ O alanine
| || aminotransferase
CH3—CH—COO- + -OOC—C—CH2—CH2—COO-
alanine -ketoglutarate
O NH3+
|| |
CH3—C—COO OOC—CH—CH2—CH2—COO-
pyruvate glutamate

58. Oxidative Deamination
Removes the amino group as an ammonium ion from glutamate.
Provides -ketoglutarate for transamination.
NH glutamate
| dehydrogenase
-OOC—CH—CH2—CH2—COO- + NAD+ + H2O
glutamate O ||
-OOC—C—CH2—CH2—COO- + NH4+ + NADH
-ketoglutarate

59. Learning Check Write the products from the transamination of
-ketoglutarate by aspartate.
NH3+ |
-OOC—CH—CH2—COO-
aspartate O ||
-OOC—C—CH2—CH2—COO-
-ketoglutarate

60. Solution Write the products from the transamination of
-ketoglutarate by aspartate. O ||
-OOC—C—CH2—COO-
oxaloacetate
NH3+ |
-OOC—CH—CH2—CH2—COO-
glutamate

61. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.8
Urea Cycle O ||
H2N—C—NH2 urea

62. Urea Cycle The urea cycle
Detoxifies ammonium ion from amino acid degradation.
Converts ammonium ion to urea in the liver. O ||
H2N—C—NH2 urea
Provides g urea daily for urine formation in the kidneys.

63. Carbamoyl Phosphate Carbamoyl phosphate is formed
In the mitochondria, when ammonium ion reacts with CO2 from the citric acid cycle, 2 ATP, and water.
carbomyl phosphate
synthetase
NH4+ + CO ATP + H2O
O O
|| ||
H2N—C—O—P—O ADP + Pi | O-
carbamoyl phosphate

64. Reaction 1 Transfer of Carbamoyl Group
In reaction 1 of the urea cycle,
The carbamoyl group is transferred to ornithine to form citrulline.
Citrulline moves across the mitochondrial membrane into the cytosol.
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65. Reaction 2 Condensation with Aspartate
In reaction 2 of the urea
cycle,
That takes place in the cytosol, citrulline combines with aspartate.
Hydrolysis of ATP to AMP provides energy.
The N in aspartate is part of urea.
Cytosol
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66. Reaction 3 Cleavage of Fumarate
In reaction 3 of the urea cycle, fumarate
Is cleaved from argininosuccinate.
Enters the citric acid cycle.
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67. Reaction 4 Hydrolysis Forms Urea
In reaction 4 of the urea
cycle,
Arginine is hydrolyzed
Urea forms.
Ornithine returns to the mitochondrion to pick up another carbamoyl group to repeat the urea cycle.
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68. Urea Cycle
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69. Summary of Urea Cycle The urea cycle converts: Ammonium ion to urea
Aspartate to Fumarate
3ATP to 2ADP, AMP, 4Pi
NH CO ATP + aspartate + 2H2O
urea + 2ADP + AMP + 4Pi + fumarate

70. Learning Check Identify the site for each as:
1) mitochondrion 2) cytosol
A. Formation of urea.
B. Formation of carbamoyl phosphate.
C. Aspartate combines with citrulline.
D. Fumarate is cleaved.
E. Citrulline forms.

71. Solution Identify the site for each as: 1) mitochondrion 2) cytosol
A. 2 Formation of urea.
B. 1 Formation of carbamoyl phosphate.
C. 2 Aspartate combines with citrulline.
D. 2 Fumarate is cleaved.
E. 1 Citrulline forms.

72. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.9
Fates of the Carbon Atoms from
Amino Acids
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73. Carbon Atoms from Amino Acids
When needed, carbon skeletons of amino acids are used
to produce energy by forming intermediates of the citric
acid cycle.
Three-carbon skeletons
alanine, serine, and cysteine pyruvate
Four-carbon skeletons
aspartate, asparagine oxaloacetate
Five-carbon skeletons
glutamine, glutamate, proline,
arginine, histidine glutamate

74. Glucogenic and Ketogenic Amino Acids
Amino acids are classified as
Glucogenic if they generate pyruvate or oxaloacete, which can be used to synthesize glucose.
Ketogenic if they generate acetoacetyl CoA or acetyl CoA, which can form ketone bodies or fatty acids.

75. Amino Acid Pathways to Citric Acid Intermediates
Ketogenic
Glucogenic
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76. Amino Acid Pathways to Pyruvate and Oxaloacetate
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77. Glucogenic Amino Acids that Form Intermediates of the Citric Acid Cycle
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78. Learning Check Match each the intermediate with the amino acid that
provides its carbon skeleton.
1) pyruvate 2) fumarate 3) -ketoglutarate
A. cysteine
B. glutamine
C. aspartate
D. serine

79. Solution Match each the intermediate with the amino acid that
provides its carbon skeleton.
1) pyruvate 2) fumarate 3) -ketoglutarate
A. 1 cysteine
B. 3 glutamine
C. 2 aspartate
D. 1 serine

80. Learning Check Identify each as glucogenic (G) or ketogenic (K)
A. alanine
B. lysine
C. phenylalanine
D. aspartate
E. glutamate

81. Solution Identify each as glucogenic (G) or ketogenic (K) A. G alanine
B. K lysine
C. K phenylalanine
D. G aspartate
E. G glutamate

82. Chapter 24 Metabolic Pathways for Lipids and Amino Acids
24.10
Synthesis of Amino Acids
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83. Sources of Amino Acids
Essential amino acids must be obtained in the diet.
Nonessential amino acids are synthesized in the body.
TABLE 24.3
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84. Synthesis of Amino Acids
In humans, transamination of compounds from glycolysis or the citric acid cycle produces nonessential amino acids.
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85. Synthesis of Glutamine
Glutamine is synthesized by adding another amino group to glutamate.
NH glutamine
| synthetase
-OOC—CH—CH2—CH2—COO- + NH3 + ATP
glutamate
NH O
| ||
-OOC—CH—CH2—CH2—C—NH2 + ADP + Pi
glutamine

86. Learning Check Match each amino acid with the intermediate needed for
its synthesis:
1) alanine 2) glutamate 3) aspartate
A. pyruvate
B. oxaloacetate
C. -ketoglutarate

87. Solution Match each amino acid with the intermediate needed for
its synthesis:
1) alanine 2) glutamate 3) aspartate
A. 1 pyruvate
B. 3 oxaloacetate
C. 2 -ketoglutarate

88. Phenylketonurea (PKU)
In phenylketonurea (PKU)
The gene that converts phenylalanine to tyrosine is defective.
Phenylalanine forms phenylpyruvate (transamination), which goes to phenylacetate (decarboxylation).
High levels of phenylacetate cause severe mental retardation.
A diet low in phenylalanine and high in tyrosine is recommended.

89. Phenylketonurea (PKU)
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90. Overview of Metabolism
In metabolism
Catabolic pathways degrade large molecules.
Anabolic pathway synthesize molecules.
Branch points determine which compounds are degraded to acetyl CoA to meet energy needs or converted to glycogen for storage.
Excess glucose is converted to body fat.
Fatty acids and amino acids are used for energy when carbohydrates are not available.
Some amino acids are produced by transamination.

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