**2. Structure of hemoglobin (Hb)**

Hemoglobin is a tetramer composed of 2-alpha (α)-globin and 2-beta (β)-globin chains working in combination with heme to transport oxygen in the blood (**Figure 1**). It is iron containing protein, synthesized inside immature erythrocyte in the red bone marrow. The globin polypeptides bind heme molecule, which in turn allows the hemoglobin in erythrocytes to bind oxygen reversibly and transport it from the lungs to other part of body [7, 8].

The main hemoglobin type is HbA in normal adult constitute about 98% and contains two alpha and two beta globin chains (α2β2). The minor type HbA2 constitute less than 3% of the adult hemoglobin consists of two alpha chains and two delta chains (α2δ2). HbF is predominant hemoglobin sub-type, found only during fetal life and consist of two alpha and two gamma (γ) subunits (α2γ2) [9, 10].

**Figure 1.** *Structure of hemoglobin [2].*
