quiz9[1] - Name 2008 Biochemistry Quiz 9 Multiple Choice(13...

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Unformatted text preview: 04/25/2008 Name: ______________________ 2008 Biochemistry Quiz 9 Multiple Choice (13 questions: front and back of page, 2 points each except as noted) Identify the choice that best completes the statement or answers the question. Calculators are not required and not permitted for this quiz. 2. Why is phosphofructokinase a better target for regulation than hexokinase? A. phosphofructokinase is a kinetically perfect enzyme with a high kcat/KM ratio B. glucose-6-phosphate is a substrate for phosphoglucomutase C. hexokinase can not be regulated due to the irreversibilty of phosphorylation D. phosphofructokinase reaction is unfavorable under physiological conditions E. phosphofructokinase operates at the diffusion controlled limit of catalysis 3. Beriberi causes elevated blood levels of which metabolites after consuming a meal rich in glucose? A. pyruvate and -ketoglutarate D. acetyl-CoA and succinyl-CoA B. lactate and oxaloacetate E. glucose and triacylglycerols C. malate and glycerol 4. Which of the following metabolites will not replenish oxaloacetate in the citric acid cycle? A. pyruvate through malic enzyme in many organisms B. phosphoenolpyruvate through phosphoenolpyruvate carboxykinase in muscle C. acetyl CoA derived from fatty acid oxidation through the citric acid cycle D. succinate derived from acetyl CoA by the glyoxylate cycle in plants E. pyruvate through pyruvate carboxylase in liver or kidney 5. 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) is an herbicide that blocks oxygen evolution and photophosphorylation. Oxygen evolution can be restored by addition of a Hill reagent, an external electron acceptor. What is the target of DCMU? A. ferredoxin:NADP+ reductase which blocks reduction to yeild NADPH B. the QN site of cytochrome b6f which blocks oxidation of plastoquinol C. the QB site in photosystem II which blocks reduction of plastoquinone D. the plastocyanin site of photosystem I which blocks plastocyanin oxidation E. the Mn cluster in photosystem II which blocks water binding 6. Why does CO2 assimilation stop shortly after illumination of plants cells is stopped? A. The Calvin cycle requires ATP and NADPH from the light reactions B. Rubisco absorbs a photon which promotes carboxylation of ribulose bisphosphate C. Rubisco is activated when the active site Mg2+ accepts an electron from plastocyanin D. The stomata are closed in the abscence of light which blocks CO2 absorption E. Rubisco activase absorbs a photon in carbamoylation of Lys201 -amino 7. What is the source of carbons for the Calvin cycle? A. acetyl-CoA D. glycogen B. carbon dioxide E. glucose C. glyoxylate 1 Name: ______________________ 8. How is rubisco activated for carbon fixation? A. Zn2+ ion is bound by carboxylate groups of a glutamate and an aspartate B. oxidation of a sulhydryl by thioredoxin to form covalent disulfide bond C. carbon dioxide is added to a lysine amine group to form a carbamate D. ribulose-1,5-phosphate forms a Schiff base intermediate with a lysine amine group E. carbon dioxide binds to a Mg2+ within a chlorophyll a prosthetic group 9. Which of the following is not true of photorespiration? A. salvages 2-phosphoglycolate B. bypasses photosystem II C. glyoxylate is an intermediate D. regenerates 3-phosphoglycerate E. consumes O2 and releases CO2 10. The oxidative pentose phosphate pathway is active in animal cells. What is not a function of the oxidative pentose phosphate pathway? A. provides NADPH and ATP when coupled to glycolysis B. provides carbon for biosynthesis by fixation of CO2 C. provides NADPH for biosynthesis D. provides ribose 5-phosphate for nucleic acid synthesis E. provides fructose 6-phosphate for sugar synthesis 11. Which of the following gluconeogenic enzymes does not have a corresponding isozyme in chloroplasts? A. triose phosphate isonmerase B. phosphoglycerate kinase C. glyceraldehyde 3-phosphate dehydrogenase D. fructose 1,6-biphosphatase E. phosphoglycerate mutase 12. Two cysteines within thioredoxin participate in activation of enzymes by reduction of disulfide bonds through a disulfide exchange reaction. How can labeled thioredoxin be used to identify these enzymes? A. thioredoxin transfers a radioactive 35S atom to the enzyme by disulfide reduction B. thioredoxin forms two long-lived disulfide bonds with the enzyme C. thioredoxin with a Cys to Ser mutation forms a thioester bond with the enzyme D. thioredoxin with a Cys to Ser mutation forms one disulfide bond with the enzyme E. thioredoxin with both Cys mutated to Ser binds irreversibly to the enzyme 13. An herbicide stops CO2 fixation by the Calvin cycle in plants through irreversible inhibition of the sedoheptulose 1,7-bisphosphatase. What effects would this herbicide have on humans? A. inhibition of the branching enzyme and deficiency in glycogen synthesis B. no effect, sedoheptulose 1,7-bisphosphatase is not found in humans C. inhibition of Complex II in the electron transport chain and ATP deficiency D. inhibition of the Calvin cycle and dihydroxyacetone phosphate deficiency E. inhibition of oxidative pentose phosphate pathway and NADPH deficiency 2 ...
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