WRITE YOUR NAME AND I.D. NUMBER LEGIBLY ON EVERY PAGE – PAGES WILL BE SEPARATED FOR GRADING! CHECK TO BE SURE YOU HAVE 6 PAGES, NAME (print): INCLUDING COVER PAGE. 5-digit course ID # I swear/affirm that I have neither given nor received any assistance with this exam. Signature: Date: BIOCHEMISTRY 460 FOURTH HOUR EXAMINATION FORM A (YELLOW) ANSWER KEY May 6, 2005 If any part of an answer is shown anywhere other than in the space provided, make a note in the space provided and put answer on back of SAME PAGE so the grader for that page will have it. IT IS CRITICAL THAT YOU PUT YOUR NAME ON EACH PAGE AS WE WILL BE SEPARATING THE EXAM FOR GRADING PURPOSES.Biochemistry 460, Exam #4 Form A ANSWERS NAME May 6, 2005 5-digit course ID# page 2 1. (5 pts) What explains the observation that people born with a deficiency in the enzyme glucose-6-phosphate dehydrogenase (G6PD) become clinically anemic if they have a diet rich in fava beans? Fava beans contain toxic compounds that must be reduced by glutathione in red blood cells to prevent cell damage. Without sufficient G6PD activity, NADPH levels produced by the pentose phosphate pathway are too low to keep glutathione in the reduced state. 2. Fructose-2,6-bisphosphate (F-2,6-BP) is an allosteric regulator of metabolic flux through the glycolytic and gluconeogenic pathways. A. (6 pts) Circle the correct label (– F-2,6-BP or + F-2,6-BP) for each of the curves in the two graphs below that indicate presence or absence of F-2,6-BP in the enzyme assay. PFK-1 is phosphofructokinase-1 and FBPase-1 is fructose-1,6-bisphosphatase. (There are 2 curves on each graph, so 4 answers total.) B. (3 pts) Circle the most correct choice between each pair of underlined words in the sentence below: Insulin / glucagon stimulates an intracellular signaling pathway that results in the dephosphorylation of F-2,6-BP leading to increased flux through the glycolytic / gluconeogenic pathway. 3. The Cori cycle provides a mechanism to replenish glycogen in muscle cells following anaerobic exercise by converting lactate, derived from muscle glycogen degradation, into glucose in liver cells. A. (3 pts) How many net ATP are generated in muscle cells per glucose-1-P under these anaerobic conditions, i.e., 1 glucose-1-P obtained from glycogen degradation ---> 2 lactate? 3 ATP (one additional net ATP because the glucose product of glycogen breakdown is already phosphorylated and the hexokinase ATP investment step is not required). B. (3 pts) How many ATP are required in muscle cells to incorporate each glucose-1-P molecule into glycogen, i.e., 1 glucose-1-P + glycogen(n) ---> glycogen(n+1)? 1 ATP (the glycogen synthase reaction uses UDP-glucose, which requires 1 ATP to replenish after each round of glucose addition to the non-reducing end of a glycogen molecule). /20Biochemistry 460, Exam #4 Form A ANSWERS NAME May 6, 2005 5-digit course ID# page 3 4. (5 pts) Why do individuals with Von Gierke's disease, which is due to a deficiency in the enzyme glucose-6-phosphatase, accumulate large amounts of glycogen in the liver? Glycogen degradation and glucose synthesis (via gluconeogenesis) in the liver is stimulated by chronic low blood glucose levels. This leads to a build-up of glucose-6-phosphate because it cannot be dephosphorylated and effluxed out of the liver. This excess glucose-6-phosphate stimulates the activity of glycogen synthase (increased rates of dephosphorylation) leading to high levels of stored glycogen. 5. (4 pts) Insulin signaling stimulates glycogen synthesis and inhibits glycogen degradation (circle the one most correct answer): a. by phosphorylating the GM regulatory subunit of protein phosphatase-1. b. by stimulating the phosphorylation of glycogen synthase. c. by stimulating the dephosphorylation of phosphorylase kinase. d. by stimulating the phosphorylation of glycogen phosphorylase. *e. both a and c. f. none of the above. 6. (6 pts) Match the phrase on the left with the letter of the answer on the right that bests matches the description of fatty acid (FA) metabolism (only one answer best matches each description): _i__ building block of FA synthesis a. palmitoyl CoA _d__ an oxidant in FA degradation pathway b. acetyl CoA carboxylase _e__ catalyzes the commitment step in FA degradation c. cytosol _j__ a reductant in FA synthesis pathway d. FAD/FADH2 _b__ catalyzes the commitment step in FA synthesis e. carnitine acyltransferase I _g__ subcellular location of FA degradation f. phosphoenolpyruvate carboxykinase g. mitochondrial matrix h. coenzyme Q (QH2) i. malonyl CoA j. NADPH/NADP+ 7. (5 pts) Explain why degradation of triacylglycerols in humans can be used to generate glucose via the gluconeogenic pathway even though fatty acid degradation does not result in net glucose production. Triacylglycerol contains glycerol which can be converted to a gluconeogenic intermediate (dihydroxyacetone phosphate; DHAP or glyceraldehyde-3-phosphate; GAP). /20Biochemistry 460, Exam #4 Form A ANSWERS NAME May 6, 2005 5-digit course ID# page 4 8. (4 pts) Fatty acid synthesis requires 14 NADPH for every molecule of palmitate that is synthesized. What two metabolic processes in the cell provide this NADPH? Pentose Phosphate Pathway and the Citrate Shuttle 9. (4 pts) Oxidation of fatty acids generates large amounts of H2O which allows desert animals such as the camel and kangaroo rat to survive extended periods of time without taking a drink of water. What are the names of the two energy conversion processes localized to the inner mitochondrial membrane that use NADH, FADH2 and ADP as substrates in reactions that result in the net production of H2O? Electron transport system (or chain) and oxidative phosphorylation (or ATP synthesis) 10. Non-fat bagels contain ~200 calories each and consists primarily of carbohydrate. Five strips of cooked bacon contain ~250 calories and consist primarily of fat and protein. Most sedentary older adults need to consume less than 2000 calories a day to maintain their weight. A. (3 pts) What is the biochemical explanation for the observation that a diet consisting only of a dozen non-fat bagels (2400 calories) and 8 glasses of water every day for four weeks results in an increase in total body fat even
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