Which statements are true regarding the citrate cycle? a. mutating histidine residue 274 of the citrate synthase enzyme to an alanine amino acid would likely eliminate or reduce the enzymatic activity of citrate synthase. b. the histidine residue would hydrogen bond to acetyl-coa throughout the reaction mechanism, stabilizing the enolate intermediate. c. aspartate would behave as an acid in this reaction mechanism. d. oxaloacetate would be repulsed from aspartic acid in the first step of the reaction mechanism.

The correct answers are option A. "Mutating histidine residue 274 of the citrate synthase enzyme to an alanine amino acid would likely eliminate or reduce the enzymatic activity of citrate synthase", B. "The histidine residue would hydrogen bond to acetyl-CoA throughout the reaction mechanism, stabilizing the enolate intermediate", and D. "Oxaloacetate would be repulsed from aspartic acid in the first step of the reaction mechanism".

Explanation:

Citrate cycle is comprised of a series of reactions used in aerobic organisms to release energy from different chemical species. In this cycle, the citrate synthase enzyme catalyzes the first reaction which is the formation of citrate by the condensation of acetyl-CoA and oxaloacetate. The enzymatic activity depends on the histidine residue 274, which acts as proton donor to the carbonyl oxygen of acetyl CoA stabilizing the enolate intermediate of citrate. Therefore, a mutating histidine residue 274 of the citrate synthase enzyme to an alanine amino acid would likely eliminate or reduce the enzymatic activity of citrate synthase, also oxaloacetate would be repulsed from aspartic acid in the first step of the reaction mechanism as a result of this modification.