What would happen to NADH levels in a cell in the first few seconds after a drug has poisoned the enzyme that combines acetyl CoA and oxaloacetate to form citrate

The correct answer is - The level of NADH will decrease

Explanation:

In the first step of the citric acid cycle or Krebs cycle, the enzyme citrate synthase catalyses the reaction in which two-carbon Acetyl CoA combines with four-carbon oxaloacetic acid to form a six-carbon compound citric acid.

If action of the enzyme citrate synthase is inhibited by poisoning, then the product citrate will not formed. As a result further oxidation process will not be occur, thus 6 out of 10 NADH wiil not be produced.