Question

Krebs' cycle starts with the formation of a six carbon compound by reaction between

• A. fumaric acid and pyruvic acid
• B. $OAA$ and acetyl $CoA$
• C. malic acid and acetyl $CoA$
• D. succinic acid and pyruvic 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 tricarboxylic $6$-carbon compound called citric acid. It is the first product of Krebs' cycle. $CoA$ is liberated.
Acetyl $CoA+$ Oxaloacetic acid $+H_{2}O$ $\stackrel{\text{citrate synthase}}{\to }$ Citrate $+CoA$