Now, step four is a very important step. Why? Well, because this is a step that actually drives this entire reaction forward. So remember, what we did in this step here is we hydrolyzed the high energy ATP molecule, and we use that energy to actually carboxylate this acetyl coenzyme A to form this malcoenzyme A. Now, what we do here is a decarboxylation step, and we break a thio ester bond. And this pretty much releases enough energy for us to actually drive this reactant forward.