As shown here, we essentially go from an open confirmation to a closed confirmation. But it's not entirely closed because we still have to be able to fit the Cetal coenzyme A so that they actually can interact with one another to form the citral coenzyme A. And once the citral coenzyme A is formed, as we'll see in just a moment, only then do we have a complete closure of these active sites. So once this conformational change takes place, it also creates a binding site for acetylco enzyme A and shifts the catalytic residues in the active side of the enzyme into their proper orientation and position so that the catalysis reaction can actually take place. So to summarize how this process of aldole condensation, basically the first process, step one of the citric acid cycle actually takes place, let's take a look at three of these three diagrams, beginning with diagram number one. Now, in diagram number one, we have the active side of our enzyme and there are three different types of residues that basically catalyze this process.