Catabolism of proteins, lipids, and carbohydrates can result in a 2-carbon molecule that enters the Krebs cycle. What is the molecule?

A) glucose

B) acetic acid or acetyl CoA

C) a fatty acid

D) an amino acid

E) pyruvate

B) acetic acid or acetyl CoA

Explanation:

At the end of glycolysis, glucose is converted into two molecules of 3carbon pyruvate. In the next step, the 3 carbon pyruvate is converted into 2 carbon compound called acetyl coenzyme A (acetyl CoA).

The acetyl CoA is the initiator of the citric acid cycle or Krebs cycle. In the respiration process, acetyl CoA is the link between glycolysis and the citric acid cycle.

The conversion of pyruvate to acetyl CoA is the oxidative decarboxylation reaction. In this reaction coenzyme NAD⁺ is e reduced to form NADH and removal of the carboxylic acid group and subsequent conversion into CO₂.