So we generate water molecules, and we also help establish a proton electrical chemical gradient that will be used by ATP synthase to actually generate those high energy ATP molecules. Now, complex four contains two important groups. One of the group are the heme groups, and the other groups are copper atoms. 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.