Hemoglobin is a protein formed of two subunits (alpha and beta) that is found in red blood cells. The protein functions to pick up oxygen and distribute it throughout the body. Both the alpha and beta subunits need to be present for the acquisition of oxygen, as does an iron molecule. Indeed, it is the presence of the iron that gives red blood cells the distinctive color that inspired their name. The presence of iron enables hemoglobin to alternatively bind oxygen and carbon dioxide.