Hemoglobin (Hb): Structure and Function
Hemoglobin is a globular, tetrameric protein consisting of four polypeptide subunits, each containing a heme group with a central ferrous iron (Fe2+) atom.
| Hb Type | Composition | Clinical Significance |
|---|---|---|
| HbA (Adult) | Alpha2 Beta2 | The primary hemoglobin in adults is about 97%. |
| HbF (Fetal) | Alpha2 Gamma2 | Higher affinity for oxygen than HbA due to lower affinity for 2,3-BPG. |
| HbA2 | Alpha2 Delta2 | Minor adult hemoglobin (about 2-3%). |
High-Yield Core Realities:
- Cooperativity: Hemoglobin exhibits positive cooperativity, meaning the binding of one O2 molecule increases the affinity of the remaining subunits for O2, resulting in a sigmoidal dissociation curve.
- T vs R State: T (Tense) state is deoxygenated, has low O2 affinity, and is stabilized by H+, CO2, and 2,3-BPG. R (Relaxed) state is oxygenated and has high O2 affinity.
- Allosteric Regulators: 2,3-BPG shifts the curve to the right (promotes unloading). High altitude and chronic hypoxia increase 2,3-BPG production to facilitate oxygen delivery to tissues.