Conversion of acetyl CoA to malonyl CoA | Crack AIIMS NOV 2016 MCQs

Which one of the following cofactors must be utilized during the conversion of acetyl CoA to malonyl CoA?

A. Thiamine pyrophosphate
B. Acyl carrier protein (ACP)
C. NADP 
D. Biotin

Answer D. Biotin

The key enzymatic step of fatty acid synthesis is the carboxylation of acetyl CoA to form malonyl CoA. The carboxyl of biotin is covalently attached to an amino acid group of a lysine residue of acetyl CoA carboxylase. The reaction occurs in two stages. In the first step, a carboxybiotin is formed: HCO3⁻+biotin-enzyme +ATP →+CO2^- biotin-enzyme +ADP +Pi. In the second step, the CO2 is transferred to acetyl CoA to produce malonyl CoA:CO2-biotin-enzyme +acetyl CoA →+malonyl CoA + biotin-enzyme. None of the other cofactors listed are involved in this reaction.