Chapter 17 Fatty Acid Catabolism
Multiple Choice Questions
1. Lipoprotein lipase acts in:
A) hydrolysis of triacylglycerols of plasma lipoproteins to supply fatty acids to various tissues.
B) intestinal uptake of dietary fat.
C) intracellular lipid breakdown of lipoproteins.
D) lipoprotein breakdown to supply needed amino acids.
E) none of the above.
2. Free fatty acids in the bloodstream are:
A) bound to hemoglobin.
B) carried by the protein serum albumin.
C) freely soluble in the aqueous phase of the blood.
D) nonexistent; the blood does not contain free fatty acids.
E) present at levels that are independent of epinephrine.
3. The role of hormone-sensitive triacylglycerol lipase is to:
A) hydrolyze lipids stored in the liver.
B) hydrolyze membrane phospholipids in hormone-producing cells.
C) hydrolyze triacylglycerols stored in adipose tissue.
D) synthesize lipids in adipose tissue.
E) synthesize triacylglycerols in the liver.
4. The glycerol produced from the hydrolysis of triacylglycerides enters glycolysis as:
A) glucose.
B) glucose-6-phosphate.
C) dihydroxyacetone phosphate.
D) pyruvate.
E) glyceryl CoA.
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5. Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires:
A) ATP, carnitine, and coenzyme A.
B) ATP, carnitine, and pyruvate dehydrogenase.
C) ATP, coenzyme A, and hexokinase.
D) ATP, coenzyme A, and pyruvate dehydrogenase.
E) carnitine, coenzyme A, and hexokinase.
6. Fatty acids are activated to acyl-CoAs and the acyl group is further transferred to carnitine because:
A) acyl-carnitines readily cross the mitochondrial inner membrane, but acyl-CoAs do not.
B) acyl-CoAs easily cross the mitochondrial membrane, but the fatty acids themselves will not.
C) carnitine is required to oxidize NAD+ to NADH.
D) fatty acids cannot be oxidized by FAD unless they are in the acyl-carnitine form.
E) None of the above is true.
7. Carnitine is:
A) a 15-carbon fatty acid.
B) an essential cofactor for the citric acid cycle.
C) essential for intracellular transport of fatty acids.
D) one of the amino acids commonly found in protein.
E) present only in carnivorous animals.
8. Which of these is able to cross the inner mitochondrial membrane?
A) Acetyl–CoA
B) Fatty acyl–carnitine
C) Fatty acyl–CoA
D) Malonyl–CoA
E) None of the above can cross.
9. What is the correct order of function of the following enzymes of -oxidation?
1. -Hydroxyacyl-CoA dehydrogenase
2. Thiolase
3. Enoyl-CoA hydratase
4. Acyl-CoA dehydrogenase
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A) 1, 2, 3, 4
B) 3, 1, 4, 2
C) 4, 3, 1, 2
D) 1, 4, 3, 2
E) 4, 2, 3, 1
10. If the 16-carbon saturated fatty acid palmitate is oxidized completely to carbon dioxide and water (via
the -oxidation pathway and the citric acid cycle), and all of the energy-conserving products are used
to drive ATP synthesis in the mitochondrion, the net yield of ATP per molecule of palmitate is:
A) 3.
B) 10.
C) 25.
D) 108.
E) 1000.
11. Saturated fatty acids are degraded by the stepwise reactions of -oxidation, producing acetyl-CoA.
Under aerobic conditions, how many ATP molecules would be produced as a consequence of removal
of each acetyl-CoA?
A) 2
B) 3
C) 4
D) 5
E) 6
12. Which of the following is (are) true of the oxidation of 1 mol of palmitate (a 16-carbon saturated fatty
acid; 16:0) by the -oxidation pathway, beginning with the free fatty acid in the cytoplasm?
1. Activation of the free fatty acid requires the equivalent of two ATPs.
2. Inorganic pyrophosphate (PPi) is produced.
3. Carnitine functions as an electron acceptor.
4. 8 mol of FADH2 are formed.
5. 8 mol of acetyl-CoA are formed.
6. There is no direct involvement of NAD+.
A) 1 and 5 only
B) 1, 2, and 5
C) 1, 2, and 6
D) 1, 3, and 5
E) 5 only
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13. Complete oxidation of 1 mole of which fatty acid would yield the most ATP?
A) 16-carbon saturated fatty acid
B) 18-carbon mono-unsaturated fatty acid
C) 16-carbon mono-unsaturated fatty acid
D) 16-carbon poly-unsaturated fatty acid
E) 14-carbon saturated fatty acid
14. Which of the following statements apply (applies) to the -oxidation of fatty acids?
1. The process takes place in the cytosol of mammalian cells.
2. Carbon atoms are removed from the acyl chain one at a time.
3. Before oxidation, fatty acids must be converted to their CoA derivatives.
4. NADP+ is the electron acceptor.
5. The products of -oxidation can directly enter the citric acid cycle for further oxidation.
A) 1 and 3 only
B) 1, 2, and 3
C) 1, 2, and 5
D) 3 and 5 only
E) 4 only
15. Which of the following statements concerning the -oxidation of fatty acids is true?
A) About 1200 ATP molecules are ultimately produced per 20-carbon fatty acid oxidized.
B) One FADH2 and two NADH are produced for each acetyl-CoA.
C) The free fatty acid must be carboxylated in the position by a biotin-dependent reaction before
the process of -oxidation commences.
D) The free fatty acid must be converted to a thioester before the process of –oxidation
commences.
E) Two NADH are produced for each acetyl-CoA.
Oxidation of fatty acids
16. The balanced equation for the degradation of CH3(CH2)10COOH via the -oxidation pathway is:
A) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoA—SH + 5H2O + ATP →
6 Acetyl-CoA + 5FADH2 + 5NADH + 5H+ + AMP + PPi
B) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoA—SH + 5H2O →
6 Acetyl-CoA + 5FADH2 + 5NADH + 5H+
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C) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoA—SH + 6H2O + ATP →
6 Acetyl-CoA + 6FADH2 + 6NADH + 6H+ + AMP + PPi
D) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoA—SH + 6H2O →
6 Acetyl-CoA + 6FADH2 + 6NADH + 6H+
Oxidation of fatty acids
17. Which compound is an intermediate of the -oxidation of fatty acids?
A) CH3—(CH2)20—CO—COOH
B) CH3—CH2—CO—CH2—CO—OPO32–
C) CH3—CH2—CO—CH2—OH
D) CH3—CH2—CO—CO—S—CoA
E) CH3—CO—CH2—CO—S—CoA
18. The conversion of palmitoyl-CoA (16:0) to myristoyl-CoA (14:0) and 1 mol of acetyl-CoA by the –
oxidation pathway results in the net formation of:
A) 1 FADH2 and 1 NADH.
B) 1 FADH2 and 1 NADPH.
C) 1 FADH2, 1 NADH, and 1 ATP.
D) 2 FADH2 and 2 NADH.
E) 2 FADH2, 2 NADH, and 1 ATP.
19. Which of the following is not true regarding the oxidation of 1 mol of palmitate (16:0) by the –
oxidation pathway?
A) 1 mol of ATP is needed.
B) 8 mol of acetyl-CoA are formed.
C) 8 mol of FADH2 are formed.
D) AMP and PPi are formed.
E) The reactions occur in the mitochondria.
20. If an aerobic organism (e.g., the bacterium E. coli) were fed each of the following four compounds as
a source of energy, the energy yield per mole from these molecules would be in the order:
A) alanine > glucose > palmitate
B) glucose > alanine > palmitate
C) glucose > palmitate > alanine
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D) palmitate > alanine > glucose
E) palmitate > glucose > alanine
21. Which of the following is (are) true of the -oxidation of long-chain fatty acids?
1. The enzyme complex that catalyzes the reaction contains biotin.
2. FADH2 serves as an electron carrier.
3. NADH serves as an electron carrier.
4. Oxidation of an 18-carbon fatty acid produces six molecules of propionyl-CoA.
5. Oxidation of a 15-carbon fatty acid produces at least one propionyl-CoA.
A) 1, 2, and 3
B) 1, 2, and 5
C) 2, 3, and 4
D) 2, 3, and 5
E) 3 and 5 only
22. The following fatty acid, in which the indicated carbon is labeled with 14C, is fed to an animal:
14CH3(CH2)9COOH
After allowing 30 minutes for fatty acid -oxidation, the label would most likely be recovered in:
A) acetyl-CoA.
B) beta-hydroxy butyryl-CoA.
C) both acetyl-CoA and propionyl-CoA.
D) palmitoyl-CoA.
E) propionyl-CoA.
23. The carbon atoms from a fatty acid with an odd number of carbons will enter the citric acid cycle as
acetyl-CoA and:
A) butyrate.
B) citrate.
C) malate.
D) succinyl-CoA.
E) -ketoglutarate.
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24. In the disease sprue, vitamin B12 (cobalamin) is poorly absorbed in the intestine, resulting in B12
deficiency. If each of the following fatty acids were in the diet, for which one would the process of
fatty acid oxidation be most affected in a patient with sprue?
A) CH3(CH2)10COOH
B) CH3(CH2)11COOH
C) CH3(CH2)12COOH
D) CH3(CH2)14COOH
E) CH3(CH2)18COOH
25. Which enzyme is the major regulatory control point for -oxidation?
A) Pyruvate carboxylase
B) Carnitine acyl transferase I
C) Acetyl CoA dehydrogenase
D) Enoyl CoA isomerase
E) Methylmalonyl CoA mutase
26. The metabolite that regulates the activity of carnitine acyl transferase I is:
A) acetyl-CoA.
B) carnitine-CoA.
C) malonyl-CoA.
D) NADH.
E) CoA.
27. Which of the following is not true about Vitamin B12?
A Vitamin B12 contains a porphyrin ring.
B) Vitamin B12 contains a carbon-cobalt bond.
C) Vitamin B12 readily undergoes homolytic bond cleavage.
D) Deficiency of Vitamin B12 causes pernicious anemia.
E) Vitamin B12 catalyzes hydrogen atom exchange with solvent H2O.
28. During -oxidation of fatty acids, ___________ is produced in peroxisomes but not in mitochondria.
A) acetyl-CoA
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B) FADH2
C) H2O
D) H2O2
E) NADH
Oxidation of fatty acids
29. When comparing the -oxidation and -oxidation pathways, which one of the following statements is
correct?
A) -oxidation and -oxidation occur in the cytoplasm.
B) -oxidation occurs at the carboxyl end of the fatty acid whereas oxidation occurs at the methyl
end.
C) -oxidation occurs at the methyl end of the fatty acid, whereas -oxidation occurs at the
carboxyl end.
D) -oxidation occurs mainly in the cytoplasm, whereas -oxidation occurs mainly in the
mitochondria.
E) -oxidation occurs mainly in the mitochondria, whereas -oxidation occurs mainly in the
cytoplasm.
30. Ketone bodies are formed in the liver and transported to the extrahepatic tissues mainly as:
A) acetoacetyl-CoA.
B) acetone.
C) -hydroxybutyric acid.
D) -hydroxybutyryl-CoA.
E) lactic acid.
31. The major site of formation of acetoacetate from fatty acids is the:
A) adipose tissue.
B) intestinal mucosa.
C) kidney.
D) liver.
E) muscle.
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Short Answer Questions
32. Why is it more efficient to store energy as lipid rather than as glycogen?
33. Explain why lipases are required in both the intestine and in the bloodstream?
34. In the first step of fatty acid oxidation, the fatty acid (R—COOH) is converted to its coenzyme A
derivative in the following reaction:
R–COOH + ATP + CoA–SH → R–CO–S–CoA + AMP + PPi
The standard free-energy change (G’) for this reaction is –15 kJ/mol
What will tend to make the reaction even more favorable when it takes place within a cell?
35. The oxidation of acetyl-CoA added to isolated, intact mitochondria is stimulated strongly by
carnitine. Why?
36. Draw the first two steps of -oxidation of saturated fatty acids. Show structures and indicate where
any cofactors participate.
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37. Draw the third and fourth steps in the -oxidation of a saturated fatty acid. Show structures, name
enzymes, and indicate where any cofactors participate.
38. One of the steps in fatty acid oxidation in mitochondria involves the addition of water across a double
bond. What is the next step in the process? Show structures and indicate where any cofactor(s)
participate(s).
39. Explain the chemical reason why the addition of water across the double bond in the second step of –
oxidation occurs with the OH adding at the -carbon, not the -carbon. Also, how does addition at
the -carbon aid in the subsequent step(s) of -oxidation?
40. In the citric acid cycle, a double bond is introduced into a four-carbon compound containing the —
CH2—CH2— group, producing fumarate. Show a similar reaction that occurs in the -oxidation
pathway.
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41. Write a balanced equation for the -oxidation of palmitoyl-CoA, a 16-carbon, fully saturated fatty
acid, and indicate how much of each product is formed.
42. For each two-carbon increase in the length of a saturated fatty acid chain, how many additional moles
of ATP can be formed upon complete oxidation of one mole of the fatty acid to CO2 and H2O?
Ans: Each —CH2—CH2— unit yields 14 extra ATP molecules. The two oxidations of the –
43. Write a balanced equation for the complete oxidation (to acetyl-CoA and any other products that
might be formed) of pelargonic acid, CH3(CH2)7COOH.
44. Describe the steps in the metabolic pathway in which cells oxidize a four-carbon, straight-chain,
saturated fatty acid (butyrate; 4:0) to the fragments that enter the citric acid cycle. Show the
structures of intermediates and products, and indicate where any cofactor(s) participate(s).
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45. Describe the steps in the metabolic pathway in which cells oxidize a five-carbon, straight-chain,
saturated fatty acid (valerate; 5:0) to the fragments that enter the citric acid cycle. Show the
structures of intermediates and products, and indicate where any cofactor(s) participate(s).
46. An experimenter studying the oxidation of fatty acids in extracts of liver found that when palmitate
(16:0) was provided as substrate, it was completely oxidized to CO2. However, when undecanoic
acid (11:0) was added as substrate, incomplete oxidation occurred unless he bubbled CO2 through the
reaction mixture. The addition of the protein avidin, which binds tightly to biotin, prevented the
complete oxidation of undecanoic acid even in the presence of CO2, although it had no effect on
palmitate oxidation. Explain these observations in light of what you know of fatty acid oxidation
reactions.
Ans: Oxidation of odd-chain fatty acid yields acetyl-CoA + propionyl-CoA. The reaction CO2 +
47. Two vitamins, biotin and vitamin B12, play crucial roles in the metabolism of propionic acid
(propionate). Explain this by showing the steps in which each is essential in propionate metabolism.
48. The total degradation of a fatty acid with an odd number of carbons yields acetyl-CoA and another
compound, X. Show the structure of X and describe the pathway by which it is converted into a citric
acid cycle intermediate, including where any cofactors participate.
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49. What are the two major differences between the -oxidation pathway in mitochondria and the –
oxidation pathway in peroxisomes?
50. Briefly explain the basic concept of –oxidation.
51. If you received a laboratory report showing the presence of a high concentration of ketone bodies in
the urine of a patient, what disease would you suspect? Why do ketone bodies accumulate in such
patients?
52. Draw the structure of one ketone body, and describe circumstances under which you would expect to
find high concentrations of this compound in the urine of a human.