Which protein within red blood cells carries oxygen by binding it to iron and is composed of four protein chains?

Which protein within red blood cells carries oxygen by binding it to iron and is composed of four protein chains?

• A. Myoglobin
• B. Fibrin
• C. Albumin
• D. Hemoglobin

Answer: (D)

This question targets understanding the oxygen-carrying protein inside red blood cells and its four-chain structure. Hemoglobin fits this description: it is a tetramer made of four polypeptide chains (two alpha and two beta in adults) and contains four heme groups, each with iron that binds one oxygen molecule. This setup allows hemoglobin to pick up oxygen in the lungs and release it in tissues, with cooperative binding that makes it efficient. Myoglobin, by contrast, is a single-chain oxygen-binding protein in muscle and does not form a tetramer, so it primarily stores oxygen rather than transports it. Fibrin is a clotting protein, and albumin is a plasma protein that helps maintain blood volume, not an oxygen carrier inside red blood cells. So the protein described is hemoglobin.

This question targets understanding the oxygen-carrying protein inside red blood cells and its four-chain structure. Hemoglobin fits this description: it is a tetramer made of four polypeptide chains (two alpha and two beta in adults) and contains four heme groups, each with iron that binds one oxygen molecule. This setup allows hemoglobin to pick up oxygen in the lungs and release it in tissues, with cooperative binding that makes it efficient. Myoglobin, by contrast, is a single-chain oxygen-binding protein in muscle and does not form a tetramer, so it primarily stores oxygen rather than transports it. Fibrin is a clotting protein, and albumin is a plasma protein that helps maintain blood volume, not an oxygen carrier inside red blood cells. So the protein described is hemoglobin.