MUSCLE PHYSIOLOGY

Detailed explanation-1: -The answer is a. acetyl CoA. The Acetyl CoA is the required substrate, starting material, or fuel for the Citric Acid Cycle or the Krebs Cycle. The Acetyl CoA is usually produced from pyruvate molecules by the action of the pyruvate dehydrogenase complex or produced from the beta-oxidation of the fatty acid.

Detailed explanation-2: -The two-carbon acetyl-CoA that is the “fuel” for the TCA cycle can be generated by several metabolic pathways including glucose metabolism, fatty acid oxidation, and the metabolism of amino acids.

Detailed explanation-3: -The citric acid cycle, where acetyl CoA is modified in the mitochondria to produce energy precursors in preparation for the next step.

Detailed explanation-4: -Acetyl-CoA, on the other hand, derived from pyruvate oxidation, or from the beta-oxidation of fatty acids, is the only fuel to enter the citric acid cycle.

Detailed explanation-5: -The TCA cycle plays a central role in the breakdown, or catabolism, of organic fuel molecules-i.e., glucose and some other sugars, fatty acids, and some amino acids. Before these rather large molecules can enter the TCA cycle they must be degraded into a two-carbon compound called acetyl coenzyme A (acetyl CoA).