In humans, the most common type of hemoglobin is hemoglobin a , which consists of 574 amino acids and has a molecular weight of 64,500 . The protein portion of the molecule, called globin, is composed of four polypeptide chains, each of which is also globular in shape. The four globin chains consist of two identical pairs: two alpha chains (141 amino acids each) and two beta chains (146 amino acids each). The non-protein portion of hemoglobin consists of four heme groups, one associated with each of the four globin chains. Hence option c is correct.

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