Homework _3

Homework _3 - Chem 481 Homework #3 Dr. Watt Due Nov. 15 at...

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Unformatted text preview: Chem 481 Homework #3 Dr. Watt Due Nov. 15 at 5pm. Name ____________________________________________________ For Homework credit answer 10 MC questions and answer 5 problems. However, you should consider the entire document as an Exam preparation document. 1. When a mixture of glucose 6‐phosphate and fructose 6‐phosphate is incubated with the enzyme phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until equilibrium is reached, the final mixture contains twice as much glucose 6‐phosphate as fructose 6‐phosphate. Which one of the following statements is best applied to this reaction outlined below? (R = 8.315 J/mol·K; T = 298 K) Glucose 6‐phosphate → fructose 6‐phosphate A) ΔG'° is incalculably large and negative. B) ΔG'° is –1.72 kJ/mol. C) ΔG'° is zero. D) ΔG'° is +1.72 kJ/mol. E) ΔG'° is incalculably large and positive. 2. In glycolysis, fructose 1,6‐bisphosphate is converted to two products with a standard free‐energy change (ΔG'°) of 23.8 kJ/mol. Under what conditions encountered in a normal cell will the free‐energy change (ΔG) be negative, enabling the reaction to proceed spontaneously to the right? A) Under standard conditions, enough energy is released to drive the reaction to the right. B) The reaction will not go to the right spontaneously under any conditions because the ΔG'° is positive. C) The reaction will proceed spontaneously to the right if there is a high concentration of products relative to the concentration of fructose 1,6‐bisphosphate. D) The reaction will proceed spontaneously to the right if there is a high concentration of fructose 1,6‐bisphosphate relative to the concentration of products. E) None of the above conditions is sufficient. 3. The standard free‐energy changes for the reactions below are given. Phosphocreatine → creatine + Pi ΔG'° = –43.0 kJ/mol ATP → ADP + Pi ΔG'° = –30.5 kJ/mol What is the overall ΔG'° for the following reaction? Phosphocreatine + ADP → creatine + ATP A) B) C) D) E) –73.5 kJ/mol –12.5 kJ/mol +12.5 kJ/mol +73.5 kJ/mol ΔG'° cannot be calculated without Keq'. 4. The hydrolysis of ATP has a large negative ΔG'°; nevertheless it is stable in solution due to: A) entropy stabilization. B) ionization of the phosphates. C) resonance stabilization. D) the hydrolysis reaction being endergonic. E) the hydrolysis reaction having a large activation energy. 5. The standard reduction potentials (E'°) for the following half reactions are given. Fumarate + 2H+ + 2e– → succinate E'° = +0.031 V FAD + 2H+ + 2e– → FADH2 E'° = –0.219 V If you mixed succinate, fumarate, FAD, and FADH2 together, all at l M concentrations and in the presence of succinate dehydrogenase, which of the following would happen initially? A) Fumarate and succinate would become oxidized; FAD and FADH2 would become reduced. B) Fumarate would become reduced, FADH2 would become oxidized. C) No reaction would occur because all reactants and products are already at their standard concentrations. D) Succinate would become oxidized, FAD would become reduced. E) Succinate would become oxidized, FADH2 would be unchanged because it is a cofactor. 6. When a muscle is stimulated to contract aerobically, less lactic acid is formed than when it contracts anaerobically because: A) glycolysis does not occur to significant extent under aerobic conditions. B) muscle is metabolically less active under aerobic than anaerobic conditions. C) the lactic acid generated is rapidly incorporated into lipids under aerobic conditions. D) under aerobic conditions in muscle, the major energy‐yielding pathway is the pentose phosphate pathway, which does not produce lactate. E) under aerobic conditions most of the pyruvate generated as a result of glycolysis is oxidized by the citric acid cycle rather than reduced to lactate. 7. Glycogen is converted to monosaccharide units by: A) B) C) D) E) glucokinase. glucose‐6‐phosphatase glycogen phosphorylase. glycogen synthase. glycogenase. 8. Which one of the following statements about gluconeogenesis is false? For starting materials, it can use carbon skeletons derived from certain amino acids. It consists entirely of the reactions of glycolysis, operating in the reverse direction. It employs the enzyme glucose 6‐phosphatase. It is one of the ways that mammals maintain normal blood glucose levels between meals. E) It requires metabolic energy (ATP or GTP). A) B) C) D) 9. Which one of the following statements about gluconeogenesis is false? F) For starting materials, it can use carbon skeletons derived from certain amino acids. G) It consists entirely of the reactions of glycolysis, operating in the reverse direction. H) It employs the enzyme glucose 6‐phosphatase. I) It is one of the ways that mammals maintain normal blood glucose levels between meals. J) It requires metabolic energy (ATP or GTP). 10. The main function of the pentose phosphate pathway is to: A) give the cell an alternative pathway should glycolysis fail. B) provide a mechanism for the utilization of the carbon skeletons of excess amino acids. C) supply energy. D) supply NADH. E) supply pentoses and NADPH. 11. Which of the following enzymes acts in the pentose phosphate pathway? A) B) C) D) E) 6‐phosphogluconate dehydrogenase Aldolase Glycogen phosphorylase Phosphofructokinase‐1 Pyruvate kinase 12. Which of the following is true of glycogen synthesis and breakdown? A) Phosphorylation activates the enzyme responsible for breakdown, and inactivates the synthetic enzyme. B) Synthesis is catalyzed by the same enzyme that catalyzes breakdown. C) The glycogen molecule “grows” at its reducing end. D) The immediate product of glycogen breakdown is free glucose. E) Under normal circumstances, glycogen synthesis and glycogen breakdown occur simultaneously and at high rates. 13. Glycogen is converted to monosaccharide units by: F) glucokinase. G) glucose‐6‐phosphatase H) glycogen phosphorylase. I) glycogen synthase. J) glycogenase. 14. The glycogen-branching enzyme catalyzes: A) degradation of (α1 → 4) linkages in glycogen B) formation of (α1 → 4) linkages in glycogen. C) formation of (α1 → 6) linkages during glycogen synthesis. D) glycogen degradation in tree branches. E) removal of unneeded glucose residues at the ends of branches. 15. Which of the below is not required for the oxidative decarboxylation of pyruvate to form acetyl‐CoA? A) B) C) D) E) ATP CoA‐SH FAD Lipoic acid NAD+ 16. In mammals, each of the following occurs during the citric acid cycle except: A) formation of α‐ketoglutarate. B) generation of NADH and FADH2. C) metabolism of acetate to carbon dioxide and water. D) net synthesis of oxaloacetate from acetylCoA. E) oxidation of acetyl‐CoA. 17. The reaction of the citric acid cycle that is most similar to the pyruvate dehydrogenase complex‐catalyzed conversion of pyruvate to acetyl‐CoA is the conversion of: A) citrate to isocitrate. B) fumarate to malate. C) malate to oxaloacetate. D) succinyl‐CoA to succinate. E) α‐ketoglutarate to succinyl‐CoA. 18. Which one of the following enzymatic activities would be decreased by thiamine deficiency? A) B) C) D) E) Fumarase Isocitrate dehydrogenase Malate dehydrogenase Succinate dehydrogenase α‐Ketoglutarate dehydrogenase complex 19. The reaction of the citric acid cycle that produces an ATP equivalent (in the form of GTP) by substrate level phosphorylation is the conversion of: A) B) C) D) E) citrate to isocitrate. fumarate to malate. malate to oxaloacetate. succinate to fumarate. succinyl‐CoA to succinate. 20. The conversion of 1 mol of pyruvate to 3 mol of CO2 via pyruvate dehydrogenase and the citric acid cycle also yields _____ mol of NADH, _____ mol of FADH2, and _____ mol of ATP (or GTP). A) B) C) D) E) 2; 2; 2 3; 1; 1 3; 2; 0 4; 1; 1 4; 2; 1 Short Answers 21. Consider the reaction: A + B → C + D. If the equilibrium constant for this reaction is a large number (say, 10,000), what do we know about the standard free‐energy change (ΔG'°) for the reaction? Describe the relationship between Keq' and ΔG'°. 22. Explain in quantitative terms the circumstances under which the following reaction can proceed. Citrate → isocitrate ΔG'° = +13.3 kJ/mol 23. During transfer of two electrons through the mitochondrial respiratory chain, the overall reaction is: NADH + 1/2 O2 + H+ → NAD+ + H2O For this reaction, the difference in reduction potentials for the two half‐reactions (ΔE'°) is +1.14 V. Show how you would calculate the standard free‐energy change, ΔG'°, for the reaction. (The Faraday constant, ℑ , is 96.48 kJ/V·mol.) 24. Explain with words, diagrams, or structures why lactate accumulates in the blood during bursts of very vigorous exercise (such as a 100‐meter dash). 25. Describe the part of the glycolytic pathway from fructose 6‐phosphate to glyceraldehyde 3‐phosphate. Show structures of intermediates, enzyme names, and indicate where any cofactors participate. 26. Describe the process of glycogen breakdown in muscle. Include a description of the structure of glycogen, the nature of the breakdown reaction and the breakdown product, and the required enzyme(s). 27. Explain the difference between homeostasis and equilibrium. 28. Explain the distinction between metabolic “regulation” and metabolic “control” in a multienzyme pathway. 29. Suppose you found an overly high level of pyruvate in a patient’s blood and urine. One possible cause is a genetic defect in the enzyme pyruvate dehydrogenase, but another plausible cause is a specific vitamin deficiency. Explain what vitamin might be deficient in the diet, and why that would account for high levels of pyruvate to be excreted in the urine. How would you determine which explanation is correct? 30. Match the cofactor with its function in the citric acid cycle. A given function may be used more than once or not at all. Cofactor Function (a) NAD+/NADH (1) carries O2 (b) FAD/FADH2 (2) carries small carbon‐containing molecules (c) CoA (3) carries e‐ (d) thiamine (4) carries small nitrogen‐containing molecules (e) biotin ...
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This note was uploaded on 03/08/2012 for the course CHEM 481 taught by Professor Wood during the Fall '10 term at BYU.

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