Question

Assume that all reactants, enzyme subunits, and cofactors (except NAD⁺) are present during the reaction catalyzed by pyruvate dehydrogenase complex. Which of the following is TRUE?

a) One round of the reaction will likely occur, but the active enzyme will not be regenerated.
b) Lipoamide will remain in the oxidized state, and the reaction will not be completed.
c) Hydroxylethyl-TPP will break down to acetyllipoamide.
d) The reaction can proceed normally: NAD⁺ is not required.
e) Lysine will no longer react with the lipoamide cofactor.

Answer 1

The correct option is a) One round of the reaction will likely occur, but the active enzyme will not be regenerated.

Step-by-step explanation:

The correct option is a) One round of the reaction will likely occur, but the active enzyme will not be regenerated.

The pyruvate dehydrogenase complex is responsible for the conversion of pyruvate to acetyl-CoA, which is an important step in cellular respiration. The complex consists of three enzymes and requires five coenzymes, including NAD⁺.

Without the presence of NAD⁺, the reaction cannot proceed normally, and the active enzyme cannot be regenerated to continue the cycle.

Therefore, if NAD⁺ is not present, only one round of the reaction is likely to occur, but the active enzyme cannot be regenerated for subsequent rounds of the reaction.