Hemoglobin found in red blood cells, is responsible for the transport of oxygen round the body. Hemoglobin has four polypeptide chains and therefor has quaternary structure. Each peptide chain possesses a globin peptide chain that is linked to a haem group, which is responsible for the characteristic red color of blood. An iron atom is located within each heam group, and each of these can combine with one molecule of oxygen.

Combination of oxygen with haemoglobin, to form oxyhaemoglobin, occurs under conditions when the concentration of oxygen is high, such as in lung alveolar capillaries. When the concentration of oxygen is low, as in the capillaries of metabolically active tissues, the bonds holding oxygen to haemoglobin become unstable and oxygen is released. This diffuses in solution into the surrounding cells. Release of oxygen from hemoglobin is called dissociation.


The amount of oxygen that can combine with hemoglobin is determined by the oxygen concentration or partial pressure.

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