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Unformatted text preview: BIS103-002 Spring 08 Question set 3 for Midterm 1 - 1 - Questions and Answers on the TCA cycle 1. To date this quarter you have encountered reactions involving the cofactors listed below: biotin lipoic acid thiamin pyrophosphate flavin adenine dinucleotide (FAD) co-enzyme A (CoA = CoASH) NAD Indicate the type of reaction that each cofactor is typically involved in. 2. Suggest a likely or possible enzyme catalyzed reaction sequence whereby -ketoadipic acid (an -keto, six carbon dicarboxylic acid) may be synthesized from acetyl CoA and -ketoglutarate. Use structures and show all cofactors (they may be abbreviated) required. Please base your answer on analogous reactions discussed this quarter. COOH | C=O | (CH 2 ) 3 | COOH 3. Malonate inhibits one enzyme of the TCA cycle. If yeast grown aerobically are incubated in the presence of malonate, succinate accumulates. What reaction does malonate inhbit? Write the name of the enzyme or write the reaction. 4. Suppose you had a patient with a much-elevated level of pyruvate in blood and urine. One possible explanation is a genetic defect in the enzyme pyruvate dehydrogenase; but another plausible explanation is a specific vitamin deficiency. Explain first what vitamin might be deficient in the diet, and why that would account for high urinary excretion of pyruvate. How would you determine which explanation is correct? 5. In a few words, what is the relationship of the pyruvate dehydrogenase complex reaction to glycolysis and the citric acid cycle? 6. Briefly describe the possible metabolic fates of pyruvate produced by glycolysis in humans and explain the circumstances that favor each. 7. At what point in the citric acid cycle does the methyl carbon from acetyl-CoA and the carbonyl carbon from oxaloacetate become chemically equivalent? carbonyl carbon from oxaloacetate become chemically equivalent?...
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- Spring '08