Hemoglobin consists of four individual polypeptide chains. We have the alpha one and alpha two chains which are identical with respect to one another. And we also have the beta one and the beta two chains, which are also identical with respect to one another. And in each one of these polypeptide chains, we have this rat structure. And these red structures are the heme groups. They contain the iron and the protoporphy that are responsible for binding diatomic oxygen.