<prompt> Which one of the following cofactors must be utilized during the conversion of acetyl CoA to malonyl CoA?Thiamine pyrophosphateAcyl carrier proteinFADBiotin  <response>: 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 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. Ref:Bender D.A. 2011. Chapter 44. Micronutrients: Vitamins Minerals. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell Eds,Harpers Illustrated Biochemistry, 29e. 