MCAT® ExamBiological and Biochemical Foundations of Living SystemsHard
A patient is diagnosed with a rare genetic disorder that results in a defect in the synthesis of hemoglobin. Specifically, the patient's hemoglobin has a reduced capacity to bind and transport oxygen, leading to symptoms of chronic fatigue and shortness of breath. Which component of hemoglobin is primarily responsible for oxygen binding?
- AGlobin protein structure
- BHeme group
- CIron atom
- D2,3-Bisphosphoglycerate (2,3-BPG)
Show answer & explanationAnswer & explanation
Correct answer: C. Iron atom
Hemoglobin is composed of four globin protein subunits, each containing a heme group. At the center of each heme group is an iron atom (Fe2+), which is the specific site where oxygen molecules reversibly bind. A defect in the oxygen-binding capacity points directly to the iron atom.
Why the other options are wrong
- A. Globin protein structure provides the framework and regulates oxygen affinity, but doesn't directly bind oxygen.
- B. The heme group is the prosthetic group containing the iron, but the iron atom itself is the direct binding site for oxygen.
- D. 2,3-BPG is an allosteric effector that reduces hemoglobin's affinity for oxygen, it does not bind oxygen itself.
Hemoglobin Oxygen Transport
Hemoglobin is a metalloprotein in red blood cells responsible for transporting oxygen from the lungs to the tissues and facilitating carbon dioxide transport back to the lungs. Each hemoglobin molecule contains four heme groups, and each heme group has a central iron atom (Fe2+) that reversibly binds one oxygen molecule.
- Tetrameric protein found in red blood cells.
- Contains four heme groups, each with a central Fe2+ atom.
- Fe2+ atom is the direct binding site for oxygen.
- Exhibits cooperative binding of oxygen.
- Oxygen affinity is affected by pH, CO2, and 2,3-BPG.
Memory trick: Heme's Iron: the 'Fe'rry for Oxygen.