<prompt> Each hemoglobin contains2 polypeptide chains with 2 heme4 polypeptide chains with 2 heme2 polypeptide chains with 4 heme4 polypeptide chains with 4 heme  <response>: Hemoglobin is a globular molecule made up of four subunits. Each subunit contains a heme moiety conjugated to a polypeptide. Heme is an iron-containing porphyrin derivative. The polypeptides are referred to collectively as the globin poion of the hemoglobin molecule. There are two pairs of polypeptides in each hemoglobin molecule. Reference: Ganongs review of Medical Physiology; 25th ed; Page: 557 