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Sp07_Exam2_Key - Multiple-Choice 3 points each 60 points...

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Unformatted text preview: Multiple-Choice, 3 points each, 60 points total For each of the following questions, encircle the letter corresponding to the BEST reSponse. I. 4. Which of the following is NOT an assumption made in the derivation of the Michaselis—Menten equation? @ B. Wh A. B. C. G? E. The reaction proceeds with a large, negative change in free energy. The rate of formation of BS is balanced by the rate of its destruction, eithertoE+S ortoP+E. The k_2 step can be ignored. Only one substrate is considered. (All of the above are assumptions usually made). ich of the following correctly defines KM? It is equal to the quantity k.f(k.. + k2) It is the dissociation constant for the enzyme-substrate complex. It is equal to mez’Z. It is the substrate concentration giving half-maximal velocity. It is equal to the quantity k-1;'(k. + k2) DiiSOpropylfluorophOSphate (DIFP) inactivates trypsin, chymotrypsin, acetylcholinesterase, and many other enzymes. What best explains the basis for this effect? A. It serves as a noncompetitive inhibitor of those enzymes. It forms a covalent bond with the —OH group of Ser. . It binds to the active site of these enzymes, preventing binding of substrate. I D. It binds to the Asp residue in the catalytic triad. E. It interferes with proton exchange by the sidechain of Lys. Which statement about a hemoglobin molecule is INCORRECT? A. B. C. D. 63) There are four polypeptide chains non-covalently associated. Each polypeptide chain is associated with one porphyrin ring. There is a total of four F e2+ atoms in oxyhemoglobin. One BPG can bind in a central cavity. HbA contains or and 5 chains. Which of the following statements about the X-ray structure of myoglobin is INCORRECT? A. There are eight regions of or helix. B. The regions between the helices frequently contain Pro or [3 turns. . There is one porphyrin ring per molecule. & One molecule of oxygen can be bound to the Fe3+ of the porphyrin ring. E. Hydrophobic amino acid residues are buried in the interior. Which of the following is an INCORRECT statement about NADJr and FAD? Fr NAUr transfers one hydrogen as a hydride ion and the other as a proton, whereas FAD accepts two hydrogens as free radicals. B. They are both derived from water-soluble vitamins. C. FAD is generally a stronger oxidant than is NAD+ (D. NAD+ contains the isoalloxazine ring system whereas FAD does not. B. Reoxidation of the reduced form of NAD+ yields more ATP than reoxidation of the reduced form of FAD. Which of the following is an allosteric enzyme of glycolysis? A. triose phosphate isomerase B. enolase C. aldolase ® hexokinase E. glyceraldehyde 3—phosphate dehydrogenase At higher concentrations of 5’-AMP, the rate of glycolysis would be expected to be ® greater than B. equal, or approximately equal to, C. less than the rate at lower concentrations of fructose 2-6 bisphosphate. A lipoprotein with a higher ratio of protein to lipid would be expected to have a density @ greater than B. equal, or approximately equal to, C. less than a lipoprotein with a lower ratio of protein to lipid. 10. Which of the following INCORRECTLY pairs a coenzyme with its function in the pyruvate dehydrogenase reaction? A. TPP : decarboxylation B. Lipoic acid : acyl transfer C. Lipoic acid : oxidation C? NAD” : ribosylation . FAD : oxidation 11. A derivative of which water-soluble vitamin is NOT required for the conversion of oc-ketoglutarate t0 succinyl CoA in the TCA cycle? A. thiamin B riboflavin C. niacin ® biotin E. pantothenic acid hwwv—O 13. Per turn of the tricarboxylic acid cycle, how many GTP is (are) produced? A. (B? C. D. E. h-UJN—‘D 14. How many protons are transported out of the mitochondrion when an electron pair passes from an FAD-linked substrate to oxygen? A. 2 B. 4 GD 6 D. 8 E. 10 15. The following reactions are involved in the catabolism of galactose in the liver: galactose + ATP = galactose l-phosphate + ADP galactose l-phosphate + UDP-glucose = UDP-galactose + glucose l-phosphate UDP-galactose = UDP-glucose glucose 1-phosphate = glucose 6-phosphate When galactose is combusted to carbon dioxide and water in a typical liver cell, what is the NET yield of ATP? Assume the glycerophosphate shuttle is operating. A. 24 B. 26 . 28 (g) 30 E. 32 16. When glyceraldehyde is combusted to carbon dioxide and water in a typical liver cell, what is the NET yield of ATP? Assume the glycerophosphate shuttle is operating. A. 12 B. 14 CE) 15 D. 18 E. 19 17. When 14CO2 is added to a suspension of Chzoreua, the first stable labeled compound that can be isolated is A. ribulose 1,5 bisphosphate B. glyceraldehyde 3-phosphate @ 3-phosphoglycerate D. xylulose S-phosphate E. ribose 5-phohphate 18. Which of the following CORRECTLY pairs 3 compound with its effects on electron transport and oxidative phosphorylation? @‘ Cyanide : Inhibitor of cyt c oxidase Carbon monoxide : Inhibitor of succinate dehydrogenasc C. Oligomycin : uncoupling agent D. 2,4 dinitrophenol : inhibitor of ATP synthase 19. Which of the following would be the expected result when dinitrophenol is added to isolated mitochondria? Electron transport would occur, but oxidative phosphorylation would not. Neither electron transport nor oxidative phosphorylation would occur. B. C. Electron transport and oxidative phosphorylation would occur, but only from FAD—linked substrates. D. Electron transport and oxidative phosphorylation would occur, but only from NAB-linked substrates. E. Electron transport and oxidative phosphorylation would occur from both FAD-linked and NAB-linked substrates. 20. Which of the following is NOT an intermediate of the glycolytic pathway? A. glyceraldehyde 3-phosphate B. pyruvate C? oxaloacetate . fructose 6-phosphate E. phosphoenolpyruvate Short Answer Credit for each item is iven in arentheses. 21. (4) Suppose an organism were found which carried out anaerobic glycolysis producing a compound, X, other than lactate or ethanol. What condition(s) must be fulfilled by the reaction(s) leading from pyruvate to X? WWW/+1)“ @r U > K 22. (3) Give the function of each of the following in the light reactions of photosynthesis. (a) photosystem I 9 NfiZDPfi ++F (b) photosystem II “#702, (c) the electron transport chain joining the two photosystems .___..'> #97? 23. (3) What would be the expected consequence on ATP synthesis and electron transport if dinitrophenol and oligomycin were added to an isolated, respiring, mitochondrial preparation? Explain briefly. [7 watt! 04am, bat n0 2477ij:0. 24. (3) When glucose labeled with 14C in its aldehydic carbon atom is added to a liver cell preparation, what carbon atom in pyruvate will be labeled? Explain briefly. 25. (4) Write a balanced equation for the conversion of glucose to lactic acid in a typical cell. . . “'3‘ =—' 2 @9114, 4,6,24/ 26. (4) Below are shown two oxygen-dissociation curves for hemoglobin. Decide which curve is appropriate for each of the following descriptors. % Sat 1302 I a) the curve at the lower concentration of BPG b) the curve at the lower pH l c) the curve at the higher pco2 7— d) Assuming one curve corresponds to HbA and the other to HbF, which is the one for HbA? 2" , 27. (4) The chymotrypsin-catalyzed hydrolysis of p—nitrophenyl acetate occurs by a two-step mechanism. The first reaction is rapid and the second is slow. (i) PNPAc + Enz = PNP + Enz-Ac (ii) Enz—Ac + H20 = Enz + Acetate (a) Sketch a plot of product vs. time for the reaction. Be sure to label the curve for each product. PM? ta He» 1: (b) Classify this reaction according to type. 27. (12) Data on the effects of an enzyme inhibitor are given in the following table. Substrate V(mmol ml" min' ) Concentration - No Inhibitor With Inhibitor 0.2 5.0 3.0 0.4 7.5 5.0 10.0 7.5 1.0 10.7 8.3 2.0 12.5 10.7 4.0 13.6 12.5 (a) Graph the data using a double-reciprocal plot. Label the line for the 7 + .— inhibited case. 5/7? ”‘1‘ (b) Classify the inhibition according to type. Vs do :07? ' (c) Provide a possible physical basis for the inhibitigu I do mPefes a): 7% 19"“ b 1 KM 27 79 E ((1) Give a kinetic mechanism for this type of inhibition. E75 358%39745 :37 '4!‘ (e) Can e mhibition be overcome by increasing substrate concentration? Answer "yes" or "no." jag (1) Calculate a value for the inhibitor constant, K, assuming that the final concentration of inhibitor was 0.2 mM. m2 WM The End ...
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