Chemistry and Biochemistry 153A Spring 2010 Final Exam Instructions: (Note that changes or additions to the usual instructions have been underlined.) You will have 3 hours to complete the exam. You may use a pencil (recommended) or blue or black ink pen to write your answers. Other color inks will not be graded. Your choice of writing utensil will not affect your ability to request a regrade. Only answers on the separate answer sheets, in the indicated space, will be graded; writing anywhere else will be ignored. Be sure to write your name and your discussion board username, if you have one, on the answer sheet. Do not write in the score boxes on your answer sheets; you will be docked points if you do. For answers with a word or sentence limit, words beyond this limit will not be read or graded. For short- or multi-answer questions, including irrelevant or wrong information or selections in your answer will cause you to lose points. Write legibly. If the grader cannot read your answer, you won’t get credit. Items you may have on your desk: - non-programmable scientific calculator, without its case or cover - writing utensil(s) - student ID ALL other items must be placed into a bag, which must be zipped up or closed and pushed completely under your chair. No hats, hoods, earphones, or cellphones are allowed. If you continue to write after ‘time’ is called, your exam will be taken and docked 10 points. Questions are printed on both sides, as are the colored answer sheets. Be sure you’ve answered all of the questions!Chem 153A Final Exam, Spring 2010 Answer sheet 1 (Gold) Page 2 of 10 Part I (100 points) – Kinetics of Enzyme Inhibition through ATP Synthase 1. (5) a. Red blood cells do not contain mitochondria. Their primary fuel source must therefore be: A. Fat B. Carbohydrate C. Protein b. Briefly explain your answer to part a in 35 words or fewer. 2. (5) You are studying metabolism in yeast, and you begin your experiments by feeding the yeast 50 mM glucose labeled at carbon 4. Among the labeled compounds, you find dihydroxyacetonephosphate (DHAP). a. Briefly explain why DHAP is labeled (in 30 words or fewer). b. Which carbon of DHAP is labeled (if the phosphorylated carbon is #3)? 3. (2) True or False? Isocitrate dehydrogenase catalyzes an oxidative decarboxylation with the help of NAD+ and TPP. 4. (2) True or False? Succinate dehydrogenase does not use NAD+ as an oxidant because the reduction potential of NAD+ is too low. 5. (2) True or False? Phosphofructokinase is an allosteric enzyme. 6. (2) True or False? Coenzyme A is a 1- or 2-electron carrier. 7. (2) True or False? Glycogen phosphorylase is regulated by both covalent modification and effector binding. 8. (20) For each of the following enzymes (1-6), select all characteristics (A-I) that match: 1) Glyceraldehyde-3-phosphate dehydrogenase 2) Pyruvate dehydrogenase complex 3) Succinyl-CoA synthetase 4) Pyruvate kinase 5) Phosphoglycerate mutase 6) Succinate dehydrogenase A. Catalyzes the replacement of a thioester with a phosphoryl attachment (formation of a mixed anhydride). B. Catalyzes a substrate-level phosphorylation. C. (The enzyme) is or becomes phosphorylated D. (The enzyme) becomes reduced E. Binds a cosubstrate F. Uses metal ion(s) in catalysis G. Is a regulatory enzyme H. Forms a Shiff base I. Uses electrostatic catalysisChem 153A Final Exam, Spring 2010 Answer sheet 1 (Gold) Page 3 of 10 9. (4) The inhibition of ATCase by CTP is an example of (choose all that apply): a. Feedback inhibition b. Product inhibition c. Competitive inhibition d. Uncompetitive inhibition e. Mixed inhibition f. Allosteric inhibition g. Homotropic effects h. Heterotropic effects 10. (29) As we discussed in class, the enzyme creatine kinase catalyzes the transfer of a phosphoryl group from ATP to creatine, yielding ADP and creatine phosphate. a. (3) The ∆G'° for the hydrolysis of creatine phosphate is -43.1 kJ/mol, and the ∆G'° for the hydrolysis of ATP is -30.5 kJ/mol. Which compound, creatine phosphate or ATP, has the higher phosphoryl transfer potential? b. (3) Calculate the ∆G'° for the creatine kinase reaction. Show your reasoning. c. (3) In class we discussed that ∆G≈0 for this rection in the cell. Briefly explain why this is true (in 10 words or fewer). d. (5) Briefly explain why ∆G≈0 is important in the creatine kinase reaction being able to buffer ATP and ADP levels. (50 words or fewer.) e. (4) Calculate the ratio of [creatine phosphate]/[creatine] in human muscle if [ATP]/[ADP] = 10. f. (3) It is common for athletes to take creatine (or creatine phosphate) as a supplement. Its consumption can lead to improvements in short duration, high intensity (anaerobic) exercise, but not longer duration (aerobic) exercise. Why would aerobic exercise not be improved by supplementation with creatine? Briefly explain in 25 words or fewer. g. (3) Would you expect creatine kinase to be a regulatory enzyme? Explain why or why not in 8 words or fewer. h. (5) Humans have four isozymes of creatine kinase. How (in general) can it benefit an organism to have isozymes? Choose all that apply. A. Different isozymes may catalyze the same type of reaction with different substrates. B. Different isozymes may be regulated differently. C. Different isozymes may function in different tissues. D. Different isozymes may catalyze different reactions using the same substrate. E. Different isozymes may have different affitinites for their substrate(s). F. Different isozymes may modify different parts of the same substrate. G. Different isozymes may function in different pathways.Chem 153A Final Exam, Spring 2010 Answer sheet 1 (Gold) Page 4 of 10 11. (22) The kinetics of citrate synthase have been well studied. The following excerpts and figures come from a study of citrate synthase published in 1969 (Shepard and Garland, Biochem. J. 114, 597). From the abstract: 1. Citrate synthase (EC 4.1.3.7) was purified 750-fold from rat liver. 2. Measurements of the Michaelis constants for the substrates of citrate synthase gave values of 16 µM for acetyl-CoA and 2 µM for oxaloacetate. a. (4) For which substrate does citrate synthase have a higher binding affinity? Why is this relevant in the cell? Briefly explain in 15 words or fewer. The activity of citrate synthase was
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