MCAT® ExamBiological and Biochemical Foundations of Living SystemsMedium
A patient is diagnosed with a rare genetic disorder where their red blood cells have a significantly reduced capacity to transport oxygen. Further investigation reveals a defect in the structure of the hemoglobin molecule, specifically affecting its ability to bind oxygen efficiently. Which of the following components of hemoglobin is directly responsible for oxygen binding?
- AThe iron ion within the heme group
- BThe globin protein chains
- CThe amino acid sequence of the alpha subunits
- DThe heme group
Show answer & explanationAnswer & explanation
Correct answer: A. The iron ion within the heme group
While the heme group and globin chains are crucial for hemoglobin's structure and function, it is specifically the iron (Fe2+) ion within the center of each heme group that directly binds to oxygen molecules.
Why the other options are wrong
- B. Globin chains provide the structural framework and regulate heme's oxygen affinity, but don't bind oxygen directly.
- C. The amino acid sequence determines the protein's structure, but the iron is the functional atom for oxygen binding.
- D. The heme group is the prosthetic group containing the iron, but the iron itself is the direct binding site for oxygen.
Hemoglobin Oxygen Transport
Hemoglobin is a metalloprotein in red blood cells that transports oxygen from the lungs to the tissues and carbon dioxide from the tissues back to the lungs.
- Tetramer of four globin subunits (usually 2 alpha, 2 beta).
- Each globin chain contains a heme group.
- Each heme group contains a central ferrous (Fe2+) iron ion.
- Oxygen reversibly binds to the Fe2+ ion.
Memory trick: Iron is the Oxygen's Identity