This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Which one of the following cofactors must be utilized during the conversion of acetyl-CoA to malonyel-CoA? 
Select and explain. 
A. Thiamine pyrophosphate, B. Acyl carrier protein (ACP), C. Biotin, D. FAD
D: FAD
Answer: D: FAD 
Explanation: FAD The key enzymatic step of fatty acid syn thesis is the carboxylation of acetyl-CoA to form malonyl-CoA. The carboxyl of biotin is covalently attached to an E-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.