What is oxyhemoglobin?

• A. Iron binds to carbon dioxide
• B. Oxygen binds to carbon dioxide
• C. Iron interacts with an oxygen molecule
• D. Hemoglobin without iron binds oxygen

Answer: (C)

Oxyhemoglobin is the oxygen-bound form of hemoglobin. It forms when an oxygen molecule binds to the iron ion in the heme group of each globin chain. The iron must be in the Fe2+ state to reversibly bind O2, allowing hemoglobin to pick up oxygen in the lungs and release it to tissues where needed. This binding is what gives oxyhemoglobin its name and function as the transport form of oxygen in the blood. The other ideas aren’t correct because carbon dioxide binds to hemoglobin at different sites to form carbaminohemoglobin, or is carried as bicarbonate in plasma, and oxygen does not bind to carbon dioxide. Also, oxygen binding requires the iron in the heme; without iron, hemoglobin cannot bind O2.