And these two proteins are myoglobin and hemoglobin. Myoglobin is a protein that consists of a single polypeptide chain and it is found in the muscle cells of our body. It is used by our muscle cells to store oxygen and give the muscle cells the oxygen when the concentration of oxygen becomes very, very low. On the other hand, hemoglobin is a protein that consists of four individual polypeptide chains. We have alpha one and alpha two, which are two identical alpha chains. And we have beta one and beta two subunits, which are also identical subunits.