So when we combine these, we form the six carbon citrate molecule. Now, the question is, what exactly is the point of forming our citrate molecule? Well, basically, the reason we form a six carbon molecule is because this citric acid cycle involves two decarboxylation processes. And so we have to add two carbon atoms, and that's exactly what we do in cytrate. So step one, oxalo acetate and acetyl coenzyme A react to form citro coenzyme A, which then reacts with water to form the citrate. The purpose of this step is to create a molecule that will ultimately undergo the decarboxylation reactions.