Now, we have two heme groups, heme A and heme A three. And we have three copper atoms. Two of these three copper atoms basically associate with one another to form the copper A, copper A center. And the third, the other copper atom we call copper B, actually associates with the heme A three to form the heme A three copper B center. And this is where we're going to basically reduce that oxygen to form water molecules, as we'll see in just a moment. So let's actually go through the steps of how this process takes place and how these electrons are transferred from the reduced cytochrome C molecules that we produced along complex three onto the oxygen to form the water molecules.