This is a two part question- do not flag-thanks! a) Anaplerotic reactions permit

Question

This is a two part question- do not flag-thanks!

a) Anaplerotic reactions permit the TCA cycle to supply intermediates to biosynthetic pathways while maintaining the proper levels of cycle intermediates. Show the sequence of reactions which result in the net synthesis of citrate from pyruvate (one of which is a prominent example of an anaplerotic reaction).

b)When the rate at which the TCA cycle operates slows, the concentration of acetyl CoA increases. Specify the effect of this metabolite on the activity of pyruvate carboxylase, and discuss the metabolic advantages this affords the cell if i) the TCA cycle is slowed due to depletion of intermediates, or ii) the cycle is slowed due to an abundant energy supply (i.e., high [ATP], [NADH]).

Explanation / Answer

a)
pyruvate + HCO3- + ATP --(pyruvate carboxylase)--> Oxaloacetate + ADP + Pi

Oxaloacetate + acetyl-CoA --(citrate synthase)--> citrate + CoA


b)
increase in acetyl-CoA would increase activity of pyruvate carboxylase to produce more oxaloacetate since acetyl-CoA is underutilized

Advantage is this reaction:
Only replenish TCA cycle intermediates when needed --> if TCA cycle is slowed down by depeletion of intermediates, the intermediates can be replenished by this reaction

at high NADH, TCA cycle enzyme citrate synthase, isocitrate dehydrogenase and alpha ketoglutatrate is inhibited

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