Now, this is the outside, the inside of our cell. So basically what happens is in this particular diagram we see that we have this space, a cavity in the inside portion of that particular transmembrane pump. And notice in this particular state it is open to the outside of the cell. So what happens is, because it's open to the outside, we have these hydrogen ions, protons which can enter this cavity. And when one of these enters the cavity, the positive charge basically interacts with a negative charge found on some type of side chain group of an amino acid. So for instance, it can interact with the CEO O negatively charged side chain group and it forms a bond.