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153CProblemSetIIIAnswers - CHEMISTRY 153C Answers to Study...

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Revised 1/5/09 1 CHEMISTRY 153C Answers to Study Questions and Problems III Winter 2009 1. Indicate the position or positions of palmitic acid you might expect to become labeled with radioactive isotope in an isolated enzyme system capable of de novo synthesis of long chain fatty acids when provided with the substrates indicated? (a) 2-[ 14 C]acetylCoA, an excess of unlabeled malonylCoA, and NADPH. (b) NADPH + H + labeled with 3 H (tritium) in the 4-position of the dihydropyridine ring plus unlabeled acetylCoA and malonylCoA. 2. It is possible to formulate a pathway whereby all of the substrates (including the reactive forms of coenzymes) needed for the biosynthesis of fatty acids as catalyzed by the fatty acyl synthase complex can be derived from citrate in the cytosol ( i.e. in the cytoplasm outside the mitochondrion). (a) Propose a series of reactions starting with citrate which might accomplish this utilizing only enzymes and coenzymes normally present in the cytosol. Use structural formulas to indicate substrates and products of the reactions except for coenzymes, for which common abbreviations may be employed. (Note that products derived from citrate may be used as reactants in other reactions if necessary. Only the reactions need be shown, not the number of times they might participate.) 1. (b) CH 3 CC H 2 H 2 H 2 CH 2 C H 2 H 2 CH 2 C * H * H * H * H * H * H * H * H * H * H * H * H * H * H COOH (This is the most likely, although one might argue for one 3 H on each position except C 1 and C 16 or possibly even only one 3 H on carbons 3, 5, 7, 9, 11, 13 and 15, depending on the assumptions made.) * CH 3 (CH 2 ) 14 COOH 1. (a)
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Revised 1/5/09 2 2.(b) List by name or structure the products of the reactions in (a) which are required as substrates for fatty acyl synthesis. 2. (b) acetylCoA, malonylCoA, NADPH + H + 2.(a) CH 3 CSCoA OOC CH 2 O COO CH 2 HO COO CH 2 C COO + ATP + CoASH + C COO + ADP + P i citrate lyase CH 2 OOC C O COO + NADH + H + malate dehydrogenase OOC CH 2 COO + NAD + OH H C OOC CH 2 COO + NADP + H C malic enzyme or malate-dehydrogenase, decarboxylating CO 2 CH 3 C COO + NADPH + H + + CO 2 ATP
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153CProblemSetIIIAnswers - CHEMISTRY 153C Answers to Study...

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