The six globin chains in humans are alpha (α), beta (β), gamma (γ), delta (δ), epsilon (ε), and zeta (ζ). These polypeptide chains combine to form various types of hemoglobin.
Overview of Globin Chains
In humans, the different globin genes encode for six distinct globin polypeptide chains. These chains vary slightly in their amino acid sequences, which accounts for the different types of hemoglobin found during development and adulthood. Each hemoglobin molecule consists of four globin chains (a tetramer).
-
Alpha (α) and Zeta (ζ) Chains: These chains have 141 amino acids each. The alpha chain is a component of adult hemoglobin (HbA), fetal hemoglobin (HbF), and HbA2. The zeta chain is expressed only in the early embryo.
-
Beta (β), Gamma (γ), Delta (δ), and Epsilon (ε) Chains: These chains have 146 amino acids each. The beta chain is present in adult hemoglobin (HbA). The gamma chain is a major component of fetal hemoglobin (HbF). The delta chain is a minor component of adult hemoglobin (HbA2). The epsilon chain is expressed only in the early embryo.
Hemoglobin Types and Globin Chain Composition
Different combinations of these globin chains result in different types of hemoglobin. Here's a brief overview:
| Hemoglobin Type | Globin Chain Composition | Stage of Development |
|---|---|---|
| HbA (Adult) | α2β2 | Adult |
| HbA2 (Adult) | α2δ2 | Adult |
| HbF (Fetal) | α2γ2 | Fetal |
| Gower I | ζ2ε2 | Embryonic |
| Gower II | α2ε2 | Embryonic |
| Portland | ζ2γ2 | Embryonic |
Significance of Different Globin Chains
The presence of different globin chains at different stages of development is crucial for efficient oxygen delivery. For example, fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA), which allows the fetus to effectively extract oxygen from the maternal circulation.
