So this step is a crucial step in fatty acid synthesis because it drives the overall reaction forward. What happens is the enzyme acyl, malno ACP condensing enzyme, basically decarboxylates this group, and that prepares these two molecules for nucleophilic attack. So this nucleophilically attacks this, and that breaks this thioester bond that releases a good amount of free energy, so lowers the free energy of this product molecule, and that helps drive the equilibrium toward the product side. So we ultimately move this acetyl group from the 16 onto the ACP, and we generate this molecule here, which we call aceto, acetoacetyl coand, acetoacetatel, ACP intermediate. So we see that the Zekerboxylation of the Melania group sets up the reaction for a nucleophilic attack that cleaves the high energy Thioester bond. This bond here and the product of this is aceto, acetyl attached onto the ACP molecule.