_Y_+30 _IMG_01_11-hemoglobin.jpg AligN=MiddlE A hemoglobin (the oxygen-carrying molecule in red blood cells) is composed of 2 kinds of protein chains. Two α (alpha) globin and two β (beta) globin chains make up the molecule. A mutation (change in DNA) in the gene for the beta chain produces abnormal hemoglobin molecules in sickle cell _SIZ_sickle_cell_mutation.html anemia.