And because one hein group binds 01:02 molecule, one hemoglobin molecule can bind in total a maximum of four diatomic oxygen molecules. Now, usually, instead of picturing our hemoglobin as consisting of four individual chains, we look at the hemoglobin as consisting of two individual dimers. One of these dimers is the alpha one, beta one dimer, and the other dimer is the alpha two beta two dimer. Remember, a dimer is simply a molecule that consists of two polypeptide chains. Now, because alpha one and because alpha one and alpha two are identical and beta one and beta two are identical, we see that alpha one beta one dimer is identical to alpha two, beta two dimer. And we'll see in just a moment why we break it down into these two dimers instead of breaking it down into four individual polypeptide chains.