A normal hemoglobin molecule consists of a tetramer, of four heme and four globin chains, with a molecular weight of 64,500 daltons. Each of the four units can bind a molecule of oxygen for transport to the body's tissues. In the image shown below, there are four monomers (2 red globin chains and 2 blue globin chains) which form the entire hemoglobin tetramer structure. The green portions represent the 4 heme groups.

A normal hemoglobin molecule is comprised of the following: