Biochemistry Exam 3 Answer Key

Exam III Biochemistry I. _________________/60 II. _________________/10 III. _________________/20 IV. _________________/10 TOTAL ________________/100 I. MULTIPLE CHOICE. (60 points; 3 points each) Choose the BEST answer to the question by WRITING the appropriate letter in the BOX to the left of each question. 1. Which of the following conversions requires more than one step? 1. alanine 2. glutamate 3. aspartate 4. proline 5. phenylalanine A. B. C. D. E. 2. 1, 2, 1, 3, 2, 4, 1 and 4 and pyruvate a-ketoglutarate oxaloacetate glutamate succinate and 4 and 5 and 5 4 5 Choose a correctly balanced equation for the degradation of CH3(CH2)9COOH via the β−oxidation pathway starting from the free fatty acid. A. B. C. CH3(CH2)9COOH + 5FAD + 5NAD+ + 6CoA-SH + 5H2O + ATP 5 Acetyl-CoA + 5FADH2 + 5NADH + 5H+ + CO2+ ADP + Pi CH3(CH2)9COOH + 5FAD + 5NAD+ + 6CoA-SH + 5H2O 5 Acetyl-CoA + 5FADH2 + 5NADH + 5H+ + CO2 CH3(CH2)9COOH + 4FAD + 4NAD+ + CoA-SH + 4H2O D. 4 acetyl-CoA + propionyl-CoA + 4FADH2 + 4NADH + 4H+ CH3(CH2)9COOH + 4FAD + 4NAD+ + 5CoA-SH + 4H2O + ATP E. 4 acetyl-CoA + propionyl-CoA + 4FADH2 + 4NADH + 4H+ + AMP + PPi CH3(CH2)9COOH + 4FAD + 4NAD+ + 5CoA-SH + 4H2O + ATP 4 acetyl-CoA + propionyl-CoA + 4FADH2 + 4NADH + 4H+ + ADP + Pi 3. Urea synthesis in mammals takes place primarily in: A. B. C. D. E. 4. ornithine aspartate glutamate adenine phenylalanine Histidine Glutamine Phenylalanine Aspartate UMP Glycine Threonine All of the above B & F All compounds except C & D B & F & G All compounds except C & D & E Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to: A. B. C. D. E. 8. decarboxylation; transamination decarboxylation; β-oxidation deamination; β-oxidation decarboxylation; electron transport decarboxylation; glycolysis Which metabolic intermediate provides free NH4+ for the production of urea from via the urea cycle? A. B. C. D. E. F. G. H. I. J. K. L. 7. oxidative oxidative reductive oxidative oxidative Which of these directly donates a nitrogen atom for the formation of urea during the urea cycle? A. B. C. D. E. 6. skeletal muscle. liver. kidney. small intestine. brain. After transamination of branched chain amino acids (BCAA) all three BCAA, along with α-ketoadipate and α-ketobutyrate, undergo ______ followed by reactions similar to those of __________. A. B. C. D. E. 5. Page 2 oxaloacetate. succinate. succinyl-CoA. pyruvate. propionate. The process of getting triglycerides from the adipose and into the mitochondria of the liver for β-oxidation is initiated by _______, then involves (in order) ______ to free fatty acids, ________, ____________, and oxidation. A. B. C. D. E. zymogen activation; fatty-acid activation; mobilization; transport zymogen activation; mobilization; fatty-acid activation; transport intestinal lipases; fatty-acid activation; transport; mobilization hormone-responsive protein kinase; mobilization; fatty-acid activation; transport hormone-responsive protein kinase; fatty-acid activation; transport; mobilization Page 3 9. If a person's urine contains unusually high concentrations of urea, which of the following diets has he or she probably been eating recently? A. B. C. D. 10. aspartate uric acid ornithine malate carbamoyl phosphate 30-34; 30-34; 30-34; 15-16; 15-16; much less much more about the about the much less than than same as same as than Which of the following statements is false in reference to the mammalian synthesis of urea? A. B. C. D. 14. only and C-3 only only and C-4 In muscle, the oxidation of branched-chain amino acids can provide a significant amount of energy. The number of net ATP equivalents per mole of Leu is ______ when burned completely to CO2 and water and the energy used for oxidative phosphorylation in the mammalian mitochondria. This is _____ than the amount of ATP from glucose. A. B. C. D. E. 13. C-1 C-1 C-3 C-4 C-3 Which substance is not involved in the production of urea via the urea bi-cycle? A. B. C. D. E. 12. high carbohydrate, very low protein low carbohydrate, very high protein high fat, very low protein high fat, high carbohydrate, no protein Under some conditions, mitochondrial preparations can be made to convert added fatty acids almost quantitatively to acetoacetic acid. If palmitate (16:0) labeled with 14C in C-3 is added to such a preparation, and acetoacetate is isolated, where in acetoacetate will the label be found? A. B. C. D. E. 11. very very very very Krebs was a major contributor to the elucidation of the pathway involved. The precursor to one of the nitrogens of urea is aspartate. The process of urea production is an energy-yielding series of reactions. The amino acid arginine is the immediate precursor to urea. The human genetic disease phenylketonuria (PKU) can result from: A. B. C. D. E. F. G. H. I. J. inability to synthesize phenylalanine. inability to catabolize ketone bodies. inability to convert phenylalanine to tyrosine. production of enzymes containing no phenylalanine. deficiency of protein in the diet. deficiency in tertrahydrobiopterin All of the above C & F A & E A & C 15. Which of these amino acids is (are) both ketogenic and glucogenic? 1. 2. 3. 4. 5. 16. Cys Ser N10-formyl-THF Ala Gly fructose > alanine > fumarate > palmitate (16:0) stearate > succinate > glucose > alanine palmitate > glucose > succinate > alanine glucose > palmitate > succinate > alanine fumarate > glucose > alanine > palmitate Which of the following statements concerning the b oxidation of fatty acids is true? A. B. C. D. 20. It yields 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 from these substrates, in terms of ATP/mole, would be in the order: A. B. C. D. E. 19. hydrolysis. deamination. oxidative deamination. reductive deamination. transamination. The degradation of tryptophan is both ketogenic and glucogenic. the products acetyl-CoA, acetoacetyl-CoA, and ______. A. B. C. D. E. 18. phenylalanine serine histidine glycine tyrosine Glutamate is metabolically converted to a-ketoglutarate and NH4+ by a process described as: A. B. C. D. E. 17. Page 4 Two NADH are produced for each acetyl-CoA. The free fatty acid must be carboxylated in the b position by a biotin-dependent reaction before the process of b oxidation commences. If electron transfer to oxygen were blocked as a result of cyanide poisoning, b oxidation would also cease because the FADH2 generated in the process (by acyl-CoA dehydrogenase) could not be oxidized. About 1200 ATP molecules are ultimately produced per 20-carbon fatty acid oxidized. E3 ligase ______. A. B. C. D. E. Attaches free ubiquitin (Ubx) to itself using ATP. Attaches Ubx to Ubiquitin-conjugating enzyme Uses the Ubx attached to E2 to add Ubx to all proteins before going to the proteosome Uses the Ubx attached to E2 to add Ubx to those proteins specific to the type of E3 ligase, of which there at many, before going to the proteosome Is a subunit of the 26S proteosome II. TRUE-FALSE. (10 points) Place a "T" of "F" in the box on the left. No other answer will be accepted. Page 5 21. Vitamin B12 is used in enzymes that need the help of a free radical to perform the chemistry that they catalyze. 22. The 26S proteosome comes in two forms, a smaller form made of a 19S core plus other proteins, or a larger form made of a 20S core plus these other proteins, which together both forms regulate proteolysis, bind to ubiquinated proteins, and unfold the protein as it removes the ubiquitin proteins. 23. In animals, acetoacetate, beta-hydroxybutyrate, and acetone are derived from hydroxy-methylglutaryl-CoA, which comes exclusively from excess fatty acid degradation when sugar is unavailable. 24. Ubiquitin can be attached to proteins using the C-terminal carboxylate and a lysine on the target protein. Then polymers are made using a specific lysine on ubiquitin prior to degradation by the proteosome. 25. Ketone bodies can arise from amino-acid degradation 26. If you had a deficiency of 2,4 dienoyl-CoA reductase there would be difficulty utilizing animal fat compared to utilizing plant oils. 27. Hormone-sensitive lipases in the adipose tissue are specific for hydrolysis of fatty acids only at certain positions of a triacylglyceride. 28. The turnover of cellular proteins destined for the lysosome are hydrolyzed by the same proteases as those destined for the proteosome. 29. The peroxisome has the same ability to degrade fatty acids to acetyl-CoA as does the mitochondria. However, the peroxisomes use the energy generated from beta-oxidation to generate heat while exporting NADH and the acetyl-CoA to the mitochondria for ATP production. The so-called P-450 enzymes in the liver are oxidases that are involved in metabolizing foreign compounds, such as drugs, for removal from the body. Physiologically, they also hydroxylate steroid hormones at various positions, which distinguish them from each other structurally and their resulting function. 30. III. SHORT ANSWER. (20 points) Give a brief answer or fill in the blanks as directed to each problem or question below. 31. If you had labeled the 14C-6 of ATP in cells that were depleted of energy, in what compound would you find the label? (2.5 pts) 32. 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 they bubbled CO2 through the reaction mixture. The addition of the protein avidin, which binds biotin avidly, prevented the complete oxidation of undecanoic acid under any circumstances, although it was without effect on palmitate oxidation. (6 pts) What is the product of β-oxidation of palmitate? What is the additional product of β-oxidation of undecanoate? What pathway requires CO2 and biotin? Page 6 How many ATP equivalents are derived from the complete oxidation of stearic acid? 33. How many ATP equivalents are derived from the complete oxidation of alinolenic acid (C18: ∆9,12,15)? NOTE: In both cases start from the free fatty acid for your calculation. (4 pt) 34. Select all the expected physiological consequences of a carnitine deficiency by putting a check in the box next to each consequence below. (4 pts) depletion of stored fat in adipose tissue high levels of circulating fatty acid chronic hypoglycemia when fasting impaired ability to produce ketone bodies inability to metabolize short‑chain fatty acids reduced ability to metabolize amino acids 35. Match each functions (A-G) to cytosolic malate dehydrogenase or mitochondrial malate dehydrogenase by putting the letters in the boxes below. (3.5 pts) Cytosolic malate dehydrogenase Mitochondrial malate dehydrogenase A B C E G D F Page 7 IV. MECHANISMS. (10 points) : 36. In the diagram, an intermediate in the transaminase mechanism is shown. For the next step of the reaction, one of the carbons is protonated. Place the hydrogen next to that carbon and draw arrows to indicate the movement of electrons to make that C-H bond. The resulting molecule is a Schiff base called a PMP=AA Schiff base. Place an arrow pointing to the bond that will be hydrolyzed in subsequent steps to release the alpha-keto acid and the PMP on the enzyme. If R = Methyl, what is the name of the resulting the resulting alpha-keto acid and what was the amino acid that started this reaction? α-keto acid Amino acid No. on Test Correct Answer 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 E D B B D or B J (L partial) D D B B B C C H A C D C C D 21 22 23 24 25 26 27 28 29 30 T T F T T F T F T F 31 uric acid 32 acetyl-CoA propionyl-CoA 33 Page 1 propionyl-CoA --> succinyl-CoA C18 --> 9 Acetyl CoA --> (9x3x2.5 for NADH)+(9x1x1.5 for FADH2)+(9x1 for GTP) = 67.5 + 13.5 + 9 = 90 - 2 (for fatty-acyl CoA Synthetase = 88 From beta oxidation: (8 roundsx2.5 for NADH) + (8x1.5 for FADH2) = 20 + 12 = 32 Total is 32 + 88 = 120 C18:Delta9,12,15 its the same from acetyl CoA except that for each odd double bond (9,15) you lose the FADH2 step of beta oxidation AND for the even double bond (12) it cost an NADH; so -[(2x1.5) + (1x2.5)] = 120 – 5.5 = 114.5 48 35 Page 2 No. on Test Correct Answer 34 X x x x 35 Cytosolic malate dehydrogenase A, B, C, D, E, F, G 36 pyruvate Mitochondrial malate dehydrogenase alanine