TCA cycle...need help!!! Not for beginning!!?

Question

a) Analerotic 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 abudant energy supply (i.e., high [ATP], [NADH]).

i'm sorry but i don't get a clue wat's being asked. If anyone can explain and analyze this ill be grateful. I'm learning biochemistry and the professor that is teaching this is so hard. I'm reading text book but not much help. Plz help!!

Answer 1

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

Answer 2

Can't help too much, but maybe I can point you in the right direction.

a) Analerotic reactions

(read about this type of reaction)

permit the TCA cycle to supply intermediates to biosynthetic pathways while maintaining the proper levels of cycle intermediates.
(this is saying that the basic compounds participating in the TCA cycle always need to be around in some quantity. The analerotic reactions sound like they provide alternative means for a cell to have compounds it needs to drive/supply other biosynthetic pathways when compounds from the TCA are scarce)

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).
(definitely look at this part of the pathway, paying attention to citrate and pyruvate, and what other pathways they might be involved in)

b) When the rate at which the TCA cycle operates slows, the concentration of acetyl CoA increases.
(I'm pretty sure TCA uses acetyl CoA, so it makes sense to me that there would be more of it around if the TCA reactions slow down)

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 abudant energy supply (i.e., high [ATP], [NADH]).
(Take a look at the pathway and the parts surrounding Acetyl CoA and pyruvate carboxylase. Think about what happens in the 2 cases i and ii.)

Gotta run, good luck

Answer 3

Anapleurotic Reactions