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Explain this difference 3 25 in addition to its role

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Unformatted text preview: bisphosphate is cleaved by aldolase at equilibrium when the initial concentration of the fructose 1,6 bisphosphate is a) 1 M b) 0.1 M c) 0.01 M, d) 1 mM e) 0.1 mM Assume ∆G˚’ is +5.73 kcal/mol. 21. Would you expect glycogen to be a reducing compound, giving a positive signal with Cu+2 or Ag+1 ions? Why? 22. Citrate inhibits phosphofructokinase and stimulates fructose 1,6 ­bisphosphatase. Why are these effects consistent with cellular strategies for regulating glucose synthesis and degradation? 23. Aminotransferases are enzymes that catalyze the removal of amino groups from amino acids to yield alpha ­keto acids. How could the action of such enzymes contribute to gluconeogenesis? Consider the utilization of alanine, aspartate, and glutamate in your answer. 24. In liver, Vmax for fructose bisphosphatase is three to four times higher than Vmax for phosphofructokinase, whereas in muscle it is about 10% of that of phosphofructokinase. Explain this difference. 3 25. In addition to its role in the action of pyruvate dehydrogenase, thiamine pyrophosphate (TPP) also serves as a cofactor for other enzymes, such as pyruvate decarboxylase, which catalyzes the nonoxidative decarboxylation of pyruvate. Propose a mechanism for the reaction catalyzed by pyruvate decarboxylase. What product would you expect? Why, in contrast to pyruvate dehydrogenase, are lipoamide and FAD not needed as cofactors for pyruvate decarboxylase? 26. Lipoic acid and FAD serve as prosthetic groups in the enzyme isocitrate dehydrogenase. Describe their possible roles in the reaction catalyzed by this enzyme. 27. In the reduction of O2 to H2O by cytochrome oxidase in complex IV, four electrons and four protons are used. How can this occur when only a single electron is transferred by a heme iron or by a copper at a time? 28. Mitchell and Moyle carrie...
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