This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General physiology, Subject name: Physiology
Each hemoglobin contains 
Select and explain. 
A. 2 polypeptide chains with 2 heme, B. 4 polypeptide chains with 2 heme, C. 2 polypeptide chains with 4 heme, D. 4 polypeptide chains with 4 heme
D: 4 polypeptide chains with 4 heme
Answer: D: 4 polypeptide chains with 4 heme 
Explanation: 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: Ganong's review of Medical Physiology; 25th ed; Page: 557