QUESTION 1 1. Which of the followings are true about PDC? PDC is inhibited by ac

Question

QUESTION 1 1. Which of the followings are true about PDC? PDC is inhibited by acetyl-CoA B. PDC use FAD as SUBSTRATE C. PDC use CoA as SUBSTRATE D. The reaction catalyzed by PDC is irreversible QUESTION 2 2. Which of the followings are true about citrate synthase? O A. It catalyzes the rate limiting step in CAC B. It needs ATP C. It synthesizes a tricarboxylic acid O D. It needs NADH QUESTION 3 3. Which of the followings are true about the fate of pyruvate? A. Pyruvate can ONLY be decarboxylated B. Pyruvate contains a OH group C. Pyruvate can be converted into malate via several steps D. Pyruvate can be decarboxylated by at least two pathways

Explanation / Answer

1. The correct answers are option A and D. Pyruvate dehydrogenase is allosterically activated by fructose-1,6-bisphosphate and inhibited by NADH and acetyl-CoA. Phosphorylation of PDH is mediated by a special regulatory enzyme, pyruvate dehydrogenase kinase.

2. The correct answer is option A. Citrate synthase catalyzes the condensation of acetyl-CoA and oxalacetate to form citryl-CoA. This reaction is easily reversible. The hydrolysis of the thioester of citryl-CoA forms citrate and regenerates the CoA.It is the rate limiting step in the cycle, and thus its activity determines the rate of the TCA
cycle.It means that the reaction catalyzed by the enzyme produces the product that is part of the name and does not require a direct input of energy from a high-energy phosphate. Thus, citrate synthase catalyzes the synthesis of citrate without using ATP to do it.

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