Chp 17

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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

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a

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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.

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b

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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.

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c

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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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c

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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.

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a

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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.

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a

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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.

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c

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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.

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b

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9. What is the correct order of function of the following enzymes of -oxidation?1. -Hydroxyacyl-CoA dehydrogenase2. Thiolase3. Enoyl-CoA hydratase4. Acyl-CoA dehydrogenase

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

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c

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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.

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d

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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

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c

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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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b

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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

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b

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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

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d

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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.

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d

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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+ 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+

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a

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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

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e

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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.

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a

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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.

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c

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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 > palmitateB) glucose > alanine > palmitate C) glucose > palmitate > alanine D) palmitate > alanine > glucose E) palmitate > glucose > alanine

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e

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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

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d

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22. The following fatty acid, in which the indicated carbon is labeled with 14C, is fed to an animal: 14CH3(CH2)9COOHAfter 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.

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e

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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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d

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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)11COOHC) CH3(CH2)12COOHD) CH3(CH2)14COOHE) CH3(CH2)18COOH

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b

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25. Which enzyme is the major regulatory control point for -oxidation?A) Pyruvate carboxylase B) Carnitine acyl transferase IC) Acetyl CoA dehydrogenaseD) Enoyl CoA isomeraseE) Methylmalonyl CoA mutase

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b

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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.

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c

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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.

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e

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28. During -oxidation of fatty acids, ___________ is produced in peroxisomes but not in mitochondria.A) acetyl-CoA B) FADH2 C) H2O D) H2O2 E) NADH

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d

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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.

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b

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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.

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c

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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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d

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32. Why is it more efficient to store energy as lipid rather than as glycogen?

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: First, the energy yield per gram of lipid (about 38 kJ/g) is more than twice that for carbohydrate (about 17 kJ/g). Second, lipid is stored as anhydrous lipid droplets, but carbohydrates such as glycogen and starch are stored hydrated, and the water of hydration roughly triples the effective weight of the carbohydrate, reducing the energy yield to about 6 kJ/g.

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33. Explain why lipases are required in both the intestine and in the bloodstream?

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Fats ingested in the diet are mostly found as triacylglycerols. In order to be taken up through the intestinal mucosa these triacylglycerols must be converted to free fatty acids by the intestinal lipases. Once in the bloodstream, the free fatty acids are again converted to triacylglycerols for transport in chylomicrons. For absorption into remote tissues from the bloodstream, the triacylglycerols must again be converted to free fatty acids, this time by lipases found in the bloodstream.

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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 + PPiThe standard free-energy change (G') for this reaction is –15 kJ/molWhat will tend to make the reaction even more favorable when it takes place within a cell?

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: The hydrolysis of PPi by inorganic pyrophosphatase, for which G' is –19 kJ/mol, makes the overall G' more negative.

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35. The oxidation of acetyl-CoA added to isolated, intact mitochondria is stimulated strongly by carnitine. Why?

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Carnitine is essential in the transport of fatty acyl groups into the mitochondrial matrix, where fatty acid oxidation occurs. Digestion, mobilization, and transport of fatsPages: 671–672 Difficulty: 1

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36. Draw the first two steps of -oxidation of saturated fatty acids. Show structures and indicate where any cofactors participate.

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The reactions are those catalyzed by fatty acyl–CoA dehydrogenase and enoyl hydratase. Note the formation of FADH2 for the first step and the addition of water across the double bond in the second step. (See Fig. 17-8a.)

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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.

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The reactions are those catalyzed by -hydroxyl-CoA dehydrogenase and thiolase. Note the formation of NADH for the third step and the cleavage of the carbon-carbon bond in a reverse Claisen condensation for the fourth step. See Fig. 17-8a.Oxidation of fatty acidsPage: 673 Difficulty: 3

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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).

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The reaction is that catalyzed by -hydroxyacyl-CoA dehydrogenase, for which NAD+ is cofactor. (See Fig. 17-8a.)

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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?

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Recall that the carbon that is to a carbonyl is readily able to become a carbanion; i.e. it is not a good electrophilic center for nucleophilic addition of a hydroxide (see Chapter 13). The -carbon, by contrast is a good electrophilic center as can be readily shown by “pushing” the electrons from the C=C double bond onto the carbonyl oxygen. Addition of the OH in the -position is useful for later steps since after oxidation of the OH to a carbonyl, the -carbon is even more susceptible to becoming a carbanion, as is needed for the reverse Claisen condensation catalyzed by thiolase.page 673

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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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This is the reaction catalyzed by acyol-CoA dehydrogenase. See Fig. 17-8a. pate 673

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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.

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The overall reaction is:Palmitoyl-CoA + 7CoA-SH + 7FAD + 7NAD+ + 7H2O 8 acetyl-CoA + 7FADH2 + 7NADH + 7H+Oxidation of fatty acidsPages: 673–675 Difficulty: 3

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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?

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: Each —CH2—CH2— unit yields 14 extra ATP molecules. The two oxidations of the -oxidation pathway produce 1 FADH2 and 1 NADH, which yield 1.5 and 2.5 ATP, respectively, by oxidative phosphorylation. The extra acetyl-CoA, when oxidized via the citric acid cycle, yields another 10 ATP equivalents: 3 NADH, 1 FADH2, and 1 ATP or GTP.pg 673-76

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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.

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The odd-chain fatty acid is first activated to the CoA derivative, then oxidized to 3 acetyl-CoA and 1 propionyl-CoA by -oxidation. The propionyl-CoA is converted to succinyl-CoA through the sequence of reactions shown in Fig. 17-12. The overall reaction is therefore:Pelargonic acid + HCO3– + ATP + 4CoASH + 3FAD + 3NAD+ 3 acetyl-CoA + succinyl-CoA + 3FADH2 + 3NADH + AMP + PPiOxidation of fatty acidsPages: 673–678

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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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: Butyrate is first activated:Butyrate + ATP + CoA—SH butyryl-CoA + AMP + PPiThen, the butyryl group is transferred to carnitine and transported into the mitochondrial matrix, where it is reconverted to the butyryl-CoA derivative. This passes through the four steps of -oxidation. (See Fig. 17-8a.).673-76

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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).

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Valerate is first activated:valerate + ATP + CoA—SH valeryl-CoA + AMP + PPiThen, the valeryl group is transferred to carnitine and transported into the mitochondrial matrix, where it is reconverted to the valeryl;-CoA derivative. This passes through the four steps of -oxidation producing acetyl-CoA and propionyl-CoA. (See Fig. 17-8a.) Propionyl-CoA would be converted to succinyl-CoA by the reaction sequence in Fig. 17-12. pg673-76

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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.

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: Oxidation of odd-chain fatty acid yields acetyl-CoA + propionyl-CoA. The reaction CO2 + propionyl-CoA methylmalonyl-CoA is catalyzed by propionyl-CoA carboxylase, a biotin-containing enzyme, which is therefore inhibited by avidin.Oxidation of fatty acidsPages: 677–678

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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.

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Biotin and vitamin B12 act as cofactors for propionyl-CoA carboxylase and methylmalonyl-CoA mutase, respectively; see Fig. 17-12 for the complete sequence of reactions.Oxidation of fatty acidsPage: 678

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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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X is propionyl-CoA, and its conversion into succinyl-CoA is accomplished by the reactions in Fig. 17-12.Oxidation of fatty acidsPage: 678

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49. What are the two major differences between the -oxidation pathway in mitochondria and the -oxidation pathway in peroxisomes?

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The first major difference lies in the detailed chemistry of the first of the four steps of -oxidation. In the mitochondria, the reduced flavin that is a product of the first step is re-oxidized via the electron transport chain. In the peroxisomes, the reduced flavin is re-oxidized by O2, thus producing H2O2. The second major difference is that the peroxisomal enzymes are much more active on longer (i.e., 26-carbons) fatty acids than the mitochondrial enzymes.Oxidation of fatty acidsPage: 682

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50. Briefly explain the basic concept of -oxidation.

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: Relatively short chain fatty acids (i.e., 10-12 carbons) are oxidized on the -end (in three steps) to form a second carboxyl group. The “double-ended” fatty acid is then taken into the mitochondria and subjected to normal -oxidation, except that the last product is not acetyl-CoA, but rather succinate or adipate.Oxidation of fatty acidsPages: 684–685

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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?

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The patient is probably an untreated diabetic, but the condition might also result from fasting. In either case, the unavailability of glucose from the blood stimulates gluconeogenesis in the liver. As the substrate for glucose formation, oxaloacetate is withdrawn from the citric acid cycle, bringing that cycle to a near halt. The fatty acids being oxidized in the liver yield acetyl-CoA, which now cannot be oxidized via the citric acid cycle. Reversal of the thiolase reaction produces acetoacetyl-CoA, which is then converted into ketone bodies and exported from the liver. (See Fig. 17-18, p. 666.)Ketone bodiesPages: 686–688

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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.

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The ketone bodies, acetoacetate, -hydroxybutyrate, and acetone (Fig. 17-19), are overproduced in untreated diabetes mellitus and during prolonged fasting, when fatty acids become the principle energy source. pages 686-688

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