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  • Haemoglobin
    • Structure of Haemoglobin
      • Primary: Haemoglobin is made up of four polypeptide chains.
      • Secondary: These polypeptide chains are wound and coiled into a helix.
      • Tertiary: Each polypeptide is folded into a precise shape, vital for its ability to carry oxygen.
      • Quartenary: All four polypeptides are linked to form a spherical molecule, and each is associated with a haem group which contains an iron ion.
    • Role and Function
      • Red blood cells contain haemoglobin, which has a varying oxygen affinity.  Each  polypeptide is associated with a haem group, and the iron ion in it can combine with 1 oxygen molecule: therefore each red blood cell can carry a total of 4 oxygen molecules.
      • In the lungs, oxygen binds to haemoglobin to form oxyhaemoglobin. This is a reversible reaction, and when oxygen dissociates from it, it returns to being haemoglobin.
      • To be efficient at transporting oxygen, haemoglobin must a) associate with oxygen readily where gas exchange takes place- in humans, the lungs. b) Readily dissociate from oxygen at the tissues requiring it
    • Partial Pressure
      • It is a measure of oxygen concentration. The greater the concentration of oxygen, the higher the partial pressure.
      • Oxygen loads onto haemoglobin where there's high partial pressure and unloads where partial pressure is low.
      • Alveoli in the lungs have high partial pressure so oxygen loads. Respiring cells release C02 which lowers the p02, so hameoglobin unloads its cells.
    • Different Haemoglobin?
      • Differences occur due to variation in shape due to slightly different sequences of amino acids.
      • Haemoglobin with a high oxygen affinity: take up oxygen easily but release it less readily. Low affinity haemoglobin take up oxygen less easily but release it readily.
      • Organisms in low oxygen environments require high affinity haemoglobin providing it has a low metabolism. Organisms with high metabolisms,in high oxygen environments require low affinity haemoglobin.


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