kupdf com lehninger principles of biochemistry test bank ch 17pdf

Chapter 17 Fatty Acid Catabolism Multiple Choice Questions Digestion, mobilization, and transport of fats Page: 632 Difficulty: Ans: A Lipoprotein lipase acts in: A) B) C) D) E) hydrolysis of triacylglycerols of plasma lipoproteins to supply fatty acids to various tissues intestinal uptake of dietary fat intracellular lipid breakdown of lipoproteins lipoprotein breakdown to supply needed amino acids none of the above Digestion, mobilization, and transport of fats Page: 634 Difficulty: Ans: B Free fatty acids in the bloodstream are: A) B) C) D) E) bound to hemoglobin carried by the protein serum albumin freely soluble in the aqueous phase of the blood nonexistent; the blood does not contain free fatty acids present at levels that are independent of epinephrine Digestion, mobilization, and transport of fats Page: 634 Difficulty: Ans: C The role of hormone-sensitive triacylglycerol lipase is to: A) B) C) D) E) hydrolyze lipids stored in the liver hydrolyze membrane phospholipids in hormone-producing cells hydrolyze triacylglycerols stored in adipose tissue synthesize lipids in adipose tissue synthesize triacylglycerols in the liver Digestion, mobilization, and transport of fats Pages: 635-636 Difficulty: Ans: A Transport of fatty acids from the cytoplasm to the mitochondrial matrix requires: A) B) C) D) E) ATP, carnitine, and coenzyme A ATP, carnitine, and pyruvate dehydrogenase ATP, coenzyme A, and hexokinase ATP, coenzyme A, and pyruvate dehydrogenase carnitine, coenzyme A, and hexokinase Chapter 17 Fatty Acid Catabolism 199 Digestion, mobilization, and transport of fats Page: 636 Difficulty: Ans: A Fatty acids are activated to acyl-CoAs and the acyl group is further transferred to carnitine because: A) B) C) D) E) acyl-carnitines readily cross the mitochondrial inner membrane, but acyl-CoAs not acyl-CoAs easily cross the mitochondrial membrane, but the fatty acids themselves will not + carnitine is required to oxidize NAD to NADH fatty acids cannot be oxidized by FAD unless they are in the acyl-carnitine form None of the above is true Digestion, mobilization, and transport of fats Page: 636 Difficulty: Ans: C Carnitine is: A) B) C) D) E) a 15-carbon fatty acid an essential cofactor for the citric acid cycle essential for intracellular transport of fatty acids one of the amino acids commonly found in protein present only in carnivorous animals Digestion, mobilization, and transport of fats Page: 636 Difficulty: Ans: B Which of these is able to cross the inner mitochondrial membrane? A) B) C) D) E) Acetyl–CoA Fatty acyl–carnitine Fatty acyl–CoA Malonyl–CoA None of the above can cross Oxidation of fatty acids Pages: 637-638 Difficulty: Ans: C What is the correct order of function of the following enzymes of β oxidation? β-Hydroxyacyl-CoA dehydrogenase Thiolase Enoyl-CoA hydratase Acyl-CoA dehydrogenase A) B) C) D) E) 1, 2, 3, 3, 1, 4, 4, 3, 1, 1, 4, 3, 4, 2, 3, 200 Chapter 17 Fatty Acid Catabolism Oxidation of fatty acids Page: 639 Difficulty: Ans: D If the 16-carbon saturated fatty acid palmitate is oxidized completely to carbon dioxide and water (via the β-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) B) C) D) E) 10 25 108 1,000 10 Oxidation of fatty acids Page: 639 Difficulty: Ans: C Saturated fatty acids are degraded by the stepwise reactions of β oxidation, producing acetyl-CoA Under aerobic conditions, how many ATP molecules would be produced as a consequence of removal of each acetyl-CoA? A) B) C) D) E) 11 Oxidation of fatty acids Pages: 634-639 Difficulty: Ans: B Which of the following is (are) true of the oxidation of mol of palmitate (a 16-carbon saturated fatty acid; 16:0) by the β-oxidation pathway, beginning with the free fatty acid in the cytoplasm? Activation of the free fatty acid requires the equivalent of two ATPs Inorganic pyrophosphate (PPi) is produced Carnitine functions as an electron acceptor mol of FADH2 are formed mol of acetyl-CoA are formed + There is no direct involvement of NAD A) B) C) D) E) and only 1, 2, and 1, 2, and 1, 3, and 5 only Chapter 17 Fatty Acid Catabolism 201 12 Oxidation of fatty acids Pages: 634-639 Difficulty: Ans: D Which of the following statements apply (applies) to the β oxidation of fatty acids? The process takes place in the cytosol of mammalian cells Carbon atoms are removed from the acyl chain one at a time Before oxidation, fatty acids must be converted to their CoA derivatives + NADP is the electron acceptor The products of β oxidation can directly enter the citric acid cycle for further oxidation A) B) C) D) E) and only 1, 2, and 1, 2, and and only only 13 Oxidation of fatty acids Pages: 634-636 Difficulty: Ans: D Which of the following statements concerning the β oxidation of fatty acids is true? A) About 1,200 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 β position by a biotin-dependent reaction before the process of β oxidation commences D) The free fatty acid must be converted to a thioester before the process of β oxidation commences E) Two NADH are produced for each acetyl-CoA 14 Oxidation of fatty acids Pages: 635-639 Difficulty: Ans: A The balanced equation for the degradation of CH3(CH2)10COOH via the β-oxidation pathway is: A) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoA—SH + 5H2O + ATP → Acetyl-CoA + 5FADH2 + 5NADH + 5H+ + AMP + PPi B) CH3(CH2)10COOH + 5FAD + 5NAD+ + 6CoA—SH + 5H2O → Acetyl-CoA + 5FADH2 + 5NADH + 5H+ C) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoA—SH + 6H2O + ATP → Acetyl-CoA + 6FADH2 + 6NADH + 6H+ + AMP + PPi D) CH3(CH2)10COOH + 6FAD + 6NAD+ + 6CoA—SH + 6H2O → Acetyl-CoA + 6FADH2 + 6NADH + 6H+ 202 Chapter 17 Fatty Acid Catabolism 15 Oxidation of fatty acids Page: 638 Difficulty: Ans: E Which compound is an intermediate of the β oxidation of fatty acids? A) B) C) D) E) CH3—(CH2)20—CO—COOH CH3—CH2—CO—CH2—CO—OPO32– CH3—CH2—CO—CH2—OH CH3—CH2—CO—CO—S—CoA CH3—CO—CH2—CO—S—CoA 16 Oxidation of fatty acids Page: 638 Difficulty: Ans: A The conversion of palmitoyl-CoA (16:0) to myristoyl-CoA (14:0) and mol of acetyl-CoA by the βoxidation pathway results in the net formation of: A) B) C) D) E) FADH2 and NADH FADH2 and NADPH FADH2, NADH, and ATP FADH2 and NADH FADH2, NADH, and ATP 17 Oxidation of fatty acids Page: 639 Difficulty: Ans: C Which of the following is not true regarding the oxidation of mol of palmitate (16:0) by the βoxidation pathway? A) B) C) D) E) mol of ATP is needed mol of acetyl-CoA are formed mol of FADH2 are formed AMP and PPi are formed The reactions occur in the mitochondria 18 Oxidation of fatty acids Page: 639 Difficulty: Ans: E 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) B) C) D) E) alanine > glucose > palmitate (16:0) glucose > alanine > palmitate glucose > palmitate > alanine palmitate > alanine > glucose palmitate > glucose > alanine Chapter 17 Fatty Acid Catabolism 203 19 Oxidation of fatty acids Pages: 639, 642 Difficulty: Ans: D Which of the following is (are) true of the β oxidation of long-chain fatty acids? The enzyme complex that catalyzes the reaction contains biotin FADH2 serves as an electron carrier NADH serves as an electron carrier Oxidation of an 18-carbon fatty acid produces six molecules of propionyl-CoA Oxidation of a 15-carbon fatty acid produces at least one propionyl-CoA A) B) C) D) E) 1, 2, and 1, 2, and 2, 3, and 2, 3, and and only 20 Oxidation of fatty acids Page: 642 Difficulty: Ans: E 14 The following fatty acid, in which the indicated carbon is labeled with C, is fed to an animal: 14 CH3(CH2)9COOH After allowing 30 minutes for fatty acid β oxidation, the label would most likely be recovered in: A) B) C) D) E) acetyl-CoA beta-hydroxy butyryl-CoA both acetyl-CoA and propionyl-CoA palmitoyl-CoA propionyl-CoA 21 Oxidation of fatty acids Page: 642 Difficulty: Ans: D The carbon atoms from a fatty acid with an odd number of carbons will enter the citric acid cycle as acetyl-CoA and: A) B) C) D) E) butyrate citrate malate succinyl-CoA α-ketoglutarate 204 Chapter 17 Fatty Acid Catabolism 22 Oxidation of fatty acids Page: 642 Difficulty: Ans: B 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) B) C) D) E) CH3(CH2)10COOH CH3(CH2)11COOH CH3(CH2)12COOH CH3(CH2)14COOH CH3(CH2)18COOH 23 Oxidation of fatty acids Page: 646 Difficulty: Ans: D During β oxidation of fatty acids, _ is produced in peroxisomes but not in mitochondria A) B) C) D) E) acetyl-CoA FADH2 H2O H2O2 NADH 24 Oxidation of fatty acids Page: 649 Difficulty: Ans: B When comparing the β-oxidation and ω-oxidation pathways, which one of the following statements is correct? A) β-oxidation and ω-oxidation occur in the cytoplasm B) β oxidation occurs at the carboxyl end of the fatty acid whereas ω oxidation occurs at the methyl end C) β oxidation occurs at the methyl end of the fatty acid whereas ω oxidation occurs at the carboxyl end D) β oxidation occurs mainly in the cytoplasm whereas ω oxidation occurs mainly in the mitochondria E) β oxidation occurs mainly in the mitochondria whereas ω oxidation occurs mainly in the cytoplasm 25 Ketone bodies Page: 650 Difficulty: Ans: C Ketone bodies are formed in the liver and transported to the extrahepatic tissues mainly as: A) B) C) D) E) acetoacetyl-CoA acetone beta-hydroxybutyric acid beta-hydroxybutyryl-CoA lactic acid Chapter 17 Fatty Acid Catabolism 205 26 Ketone bodies Page: 650 Difficulty: Ans: D The major site of formation of acetoacetate from fatty acids is the: A) B) C) D) E) adipose tissue intestinal mucosa kidney liver muscle Short Answer Questions 27 Digestion, mobilization, and transport of fats Page: 631 Difficulty: Why is it more efficient to store energy as lipid rather than as glycogen? Ans: 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 kJ/g 28 Digestion, mobilization, and transport of fats Page: 635 Difficulty: 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 more favorable when it takes place within a cell? Ans: The hydrolysis of PPi by inorganic pyrophosphatase, for which ∆G'° is –19 kJ/mol, makes the overall ∆G'° more negative 29 Digestion, mobilization, and transport of fats Page: 636 Difficulty: The oxidation of acetyl-CoA added to isolated, intact mitochondria is stimulated strongly by carnitine Why? Ans: Carnitine is essential in the transport of fatty acyl groups into the mitochondrial matrix, where fatty acid oxidation occurs 206 Chapter 17 Fatty Acid Catabolism 30 Oxidation of fatty acids Page: 638 Difficulty: The β oxidation of fatty acids begins with this activation reaction: R–CH2–CH2–CH2–COOH + ATP + CoA–SH→ R–CH2–CH2–CH2–CO–S–CoA + AMP + PPi What are the next two steps (after transport into the mitochondria)? Show structures and indicate where any cofactors participate Ans: The reactions are those catalyzed by fatty acyl–CoA dehydrogenase and enoyl hydratase See Fig 17-8a, p 638 31 Oxidation of fatty acids Page: 638 Difficulty: Draw the four basic steps in the oxidation of a saturated fatty acid (the β-oxidation pathway) Show structures, name enzymes, and indicate where any cofactors participate Ans: See Fig 17-8a, p 638 32 Oxidation of fatty acids Page: 638 Difficulty: Show the last step in the sequence of the four reactions in the β-oxidation pathway for fatty acid degradation Include the structures of reactant and product, the enzyme name, and indicate where any cofactors participate Ans: See the thiolase reaction, Fig 17-8a, p 638 33 Oxidation of fatty acids Page: 638 Difficulty: 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) Ans: The reaction is that catalyzed by β-hydroxyacyl-CoA dehydrogenase, for which NAD+ is cofactor See Fig 17-8a, p 638 34 Oxidation of fatty acids Page: 638 Difficulty: 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 β-oxidation pathway Ans: See Fig 17-8a, p 638 35 Oxidation of fatty acids Page: 639 Difficulty: Write a balanced equation for the β oxidation of palmitoyl-CoA, a 16-carbon, fully saturated fatty acid, and indicate how much of each product is formed Chapter 17 Fatty Acid Catabolism 207 Ans: The overall reaction is: Palmitoyl-CoA + 7CoA-SH + 7FAD + 7NAD+ + 7H2O → acetyl-CoA + 7FADH2 + 7NADH + 7H+ 36 Oxidation of fatty acids Page: 639 Difficulty: 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 βoxidation pathway produce FADH2 and 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: NADH, FADH2, and ATP or GTP 37 Oxidation of fatty acids Pages: 639, 642 Difficulty: 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 Ans: The odd-chain fatty acid is first activated to the CoA derivative, then oxidized to acetyl-CoA and propionyl-CoA by β oxidation The propionyl-CoA is converted to succinyl-CoA through the sequence of reactions shown on p 642, Fig 17-11 The overall reaction is therefore: – + Pelargonic acid + HCO3 + ATP + 4CoASH + 3FAD + 3NAD → acetyl-CoA + succinyl-CoA + 3FADH2 + 3NADH + AMP + PPi 38 Oxidation of fatty acids Pages: 639, 642 Difficulty: (a) 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) (b) In what way would you change or add to your answer if the starting fatty acid had been five carbons long (also straight-chain and saturated)? Ans: (a) Butyrate is first activated: Butyrate + ATP + CoA—SH → butyryl-CoA + AMP + PPi Then, 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 β oxidation (See Fig 17-8a, p 638.) (b) A five-carbon chain would undergo activation and one cycle of β oxidation, producing acetyl-CoA and propionyl-CoA Propionyl-CoA would be converted to succinyl-CoA by the reaction sequence in Fig 17-11, p 642 39 Oxidation of fatty acids Pages: 639, 642 Difficulty: 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 208 Chapter 17 Fatty Acid Catabolism 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 + propionyl-CoA → methylmalonyl-CoA is catalyzed by propionyl-CoA carboxylase, a biotincontaining enzyme, which is therefore inhibited by avidin 40 Oxidation of fatty acids Page: 642 Difficulty: 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 Ans: Biotin and vitamin B12 act as cofactors for propionyl-CoA carboxylase and methylmalonyl-CoA mutase, respectively; see Fig 17-11, p 642, for the complete sequence of reactions 41 Oxidation of fatty acids Page: 642 Difficulty: 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 Ans: X is propionyl-CoA, and its conversion into succinyl-CoA is accomplished by the reactions in Fig 17-11, p 642 42 Oxidation of fatty acids Page: 642 Difficulty: Show the shortest pathway by which propionyl-CoA can be converted into a citric acid cycle intermediate Indicate where any cofactors participate Ans: See Fig 17-11, p 642 43 Ketone bodies Page: 652 Difficulty: 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 ketone bodies accumulate in such patients? Ans: 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 acetoacetylCoA, which is then converted into ketone bodies and exported from the liver See Fig 17-18, p 651 Chapter 17 Fatty Acid Catabolism 209 44 Ketone bodies Pages: 651-652 Difficulty: 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 Ans: The ketone bodies, acetoacetate, β-hydroxybutyrate, and acetone (p 615), are overproduced in untreated diabetes mellitus and during prolonged fasting, when fatty acids become the principle energy source 45 Ketone bodies Pages: 651-652 Difficulty: What are ketone bodies and why they form during fasting? Ans: The ketone bodies, acetoacetate, β-hydroxybutyrate, and acetone, are overproduced during fasting, when fatty acids from stored triacylglycerols become the principle oxidizable fuel Accumulation of acetyl-CoA and its precursor acetoacetyl-CoA favors ketone body formation Because oxaloacetate is used for gluconeogenesis, it is withdrawn from the citric acid cycle, bringing that cycle to a near halt The acetyl-CoA that is produced by β oxidation can no longer be oxidized via the citric acid cycle so it accumulates