The oxygen delivery function of Hb, that is its ability to "pick up" oxygen at the lungs and "release" it to tissue cells is made possible by minute conformational changes in quaternary structure that occur in the hemoglobin molecule and which alter the affinity of the heme pocket for oxygen. The oxygen-binding site of Hb is the heme pocket present in each of the four polypeptide chains a single atom of oxygen forms a reversible bond with the ferrous iron at each of these sites, so a molecule of Hb binds four oxygen molecules the product is oxyhemoglobin (O 2Hb). Thus heme is a metallo-porphyrin, incidentally responsible for the red color of blood.įIGURE 1: Schematic of oxygenated hemoglobin (HbA) structure
The hemoglobin (Hb) molecule is roughly spherical and comprises two pairs of dissimilar subunits (FIGURE 1).Įach of the subunits is a folded polypeptide chain (the globin portion) with a heme group (derived from porphyrin) attached.Īt the center of each heme group is a single atom of iron in the ferrous (Fe 2+) state. Each of the 5 × 1010 erythrocytes normally present in 1 mL of blood contains around 280 million hemoglobin molecules. These vital gas transport functions are dependent on the protein hemoglobin contained in erythrocytes (red blood cells).
As oxygen is consumed during cell metabolism, carbon dioxide is produced.Ī principle function of blood is the delivery of oxygen (O 2), present in inspired air, from the lungs to every cell in the body and delivery of carbon dioxide (CO 2) from cells to the lungs, for elimination from the body in expired air. Normal cell function depends on a continuous supply of oxygen.
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