Revised 9/17/03 1 CHEMISTRY 153C Study Questions and Problems II Winter 2001 1. Compare a reaction selected from the -oxidation cycle of fatty acid oxidation or the biosynthesis of acetoacetate with a closely analogous reaction of the tricarboxylic acid cycle. Select reactions for comparison in which the chemical changes involved and the mechanistic features bear a close resemblance to one another. Illustrate the reactions and comment on the most important features they have in common. 2. Illustrate with structural formulas one reaction of physiological importance for each of the following cases. Coenzymes may be abbreviated in standard fashion; intermediates and mechanisms need not be indicated. In each case state briefly a function in metabolism for the reaction you have shown. a) A reaction catalyzed by pyrophosphatase. b) A reaction in which carnitine participates as a substrate. c) A reaction catalyzed by malate synthase. 3. Unless otherwise indicated, use structural formulas for reactants and products except for coenzymes which can be abbreviated in standard fashion: a) Illustrate a reaction that is catalyzed by heart cells but not liver cells and is responsible for the ability of heart cells to use ketone bodies as an energy source. b) Would an auxiliary enzyme (or enzymes) be required to effect the complete oxidation of the activated fatty acid shown below to acetylCoA by -oxidation? CH3(CH2)5CH (CH2)10OHCOSCoA c) Show the structure of 3-hydroxy-3-methylglutarylCoA and indicate clearly with an asterisk the labeling pattern expected in this substance when it is produced in liver mitochondria that are carrying out the oxidation of 2-[14C]-palmitoylCoA.Revised 9/17/03 2 CH3CH2(CH2CH2)6CH2CSCoAO* 4. The cleavage of acetoacetylCoA to 2 acetylCoA catalyzed by the enzyme 3-ketothiolase is thermodynamically favorable under standard state conditions ( Go = -6.7 kcal mol-1). If this is the case, how could the proposed synthesis of acetoacetylCoA from acetylCoA in a reaction catalyzed by 3-ketothiolase serve as a step in the biosynthesis of ketone bodies in liver mitochondria? Be as specific as you can in describing factors that may be involved. 5. For some years after the general features of the process of -oxidation of fatty acids to acetylCoA had been elucidated, it was assumed by many biochemists that fatty acid biosynthesis from acetylCoA would be accomplished by the reversal of the -oxidation pathway. However, experimental efforts to demonstrate this were fruitless. What features of the -oxidation pathway would appear to make it a poor candidate as the scheme for the biosynthesis of fatty acids when operating in the reverse direction? 6. Illustrate how the following transformation may occur in a bacterial culture growing on acetate as a sole carbon source. More than one enzyme-catalyzed reaction may be involved. Note that this is not a balanced equation. Illustrate reactions in sequential fashion, using structures for reactants and products except for coenzymes, which may be abbreviated in standard fashion. Mechanisms are not required. CH3COSCoAHCCH2COO-CCOO-HO HCOO-HO C HCOO-CH2COO-COO-CH2CH2COO-++ 7. (a) Illustrate a pathway that shows the transformation of R-3-hydroxybutyrate to an intermediate, or intermediates, of the central metabolic pathways in heart cells. Use structures for reactants and products except for coenzymes, which may be abbreviated in the normal way. (Note: it is not necessary to show any reaction in the central pathways.) CH3COHCH2HCOO-Revised 9/17/03 3 (b) How many molecules of ATP, or its equivalent, would be synthesized during the complete oxidation of one molecule of R-3-hydroxybutyrate to 4CO2 and water in actively respiring heart cells? Briefly justify how you arrived at this number. 8. For the following transformation, calculate the net yield (+) or net consumption (-) of ATP molecules (or its equivalent e.g. GTP) that would result from the operation of that process. Assume that any reduced coenzymes produced would be reoxidized in the mitochondrion as a part of that process. Justify your answer by summarizing in a table the sources of ATP molecules produced (+) or utilized (-). It is not necessary to show individual reactions or equations; just give a brief indication of how you arrived at the number. liver4CH3COCOO-CH2 palmitic acid (C16) 9. Provide concise answers for each of the following. a) Fumarate and acetylCoA are the intermediates of the central metabolic pathways that are formed from the catabolism of tyrosine in liver. Would tyrosine fed to a diabetic animal be ketogenic, glucogenic, both ketogenic and glucogenic, or neither? Briefly explain the reasons for your answer. b) The wild type strain of a particular bacterium can grow on acetate as a sole carbon source. A mutant strain of this bacterium was obtained that was deficient in the ability to synthesize a functional isocitrate lyase enzyme. Indicate whether this mutant strain will be able to grow on acetate as a sole carbon source and briefly explain the basis for your answer. 10. Sustained oxidation of fatty acids as a major carbon and energy source during growth requires a simultaneous anaplerotic reaction other than the normal operation of the cycle reactions themselves to replenish the pool of dicarboxylic acids of the tricarboxylic acid cycle. For each of the following situations indicate the immediate enzyme-catalyzed reaction (using structures except for coenzymes, which may be abbreviated in standard fashion) which would be serving to replenish the pool of one of the dicarboxylic acids of the TCA cycle. If no replenishment reaction would be occurring indicate NONE.Revised 9/17/03 4 (a) Oxidation of normal fatty acids in a bacterial cell adapted to growth on fatty acids as a sole carbon source. (b) Oxidation of a mixture of fatty acids containing some odd-carbon fatty acids as the major carbon source in a mammalian cell. (c) Oxidation of fatty acids as a major carbon source in a mammalian cell also carrying out the catabolism of