Question

The first stable compound formed in Krebs' cycle is

• A. acetyl CoA
• B. citric acid
• C. oxaloacetic acid
• D. fumaric acid.

Answer 1

Answer: (B)

Acetyl CoA (2-carbon compound) combines with oxaloacetate (4-carbon compound) in the presence of condensing enzyme citrate synthase to form a tricarboxy lie acid 6-carbon compound called citric acid. It is the first product of Krebs' cycle. CoA is liberated.
Acetyl CoA + Oxaloacetate + $H_{2}O\stackrel{\text{Citrate Synthase}}{\to }$ Citrate +CoA