Unit 1 Section 5.5 Haemoglobin

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  • Haemoglobin
    • Haemoglobin and oxyhaemoglobin
      • human haemoglobin is found in red blood cells, its role is to carry oxygen around the body.
      • Haemoglobin is a large protein with a quaternary structure - its made up of four polypeptide chains
      • each chain has a haem group which contains iron and gives haemoglobin its red colour
      • each molecule of human haemoglobin can carry four oxygen molecules
      • in the lungs, oxygen joins to the iron in haemoglobin to form oxyhaemoglobin
        • this is a reversible reaction - near the body cells, oxygen leaves oxyhaemoglobin and it turns back to haemoglobin
          • when an oxygen molecule joins to haemoglobin its referred to as association or loading, and when oxygen leaves oxyhaemoglobin its referred to as dissociation or unloading
    • Affinity for Oxygen and pO
      • affinity for oxygen means the tendency a molecule has to bind with oxygen
      • haemoglobin's affinity for oxygen varies depending on the conditions its in - one of the conditions that affects it is the partial pressure of oxygen (pO )
      • pO  is a measure of oxygen concentration. the greater the concentration of dissolved oxygen in cells, the higher the partial pressure
      • as pO  increases, haemoglobin's affinity for oxygen also increases
        • Oxygen loads onto haemoglobin to form oxyhaemoglobin where theres a high pO
        • Oxyhaemoglobin unloads its oxygen where there's a lower pO
    • Dissociation Curves
      • an oxygen dissociation curve shows how saturated the haemoglobin is with oxygen at any given partial pressure
      • the affinity of haemoglobin for oxygen affects how saturated the haemoglobin is
    • fetal Haemoglobin
      • adult haemoglobin and fetal haemoglobin have different affinities for oxygen
      • Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin
    • Carbon Dioxide Concentration
      • the partial pressure of carbon dioxide (pCO  ) is a measure of the concentration of CO2 in a cell
      • to complicate matters, pCO also affects oxygen unloading. haemoglobin gives up its oxygen more readily at a higher pCO  .
      • its a cunning way of getting more O2 to cells during activity
      • when cells respire they produce carbon dioxide which raises the pCO2
      • this increases the rate of oxygen unloading - the dissociation curve 'shifts' right. the saturation of blood with oxygen is lower for a given pO2 meaning that more oxygen is being released. this is called the BOHR EFFECT.
      • The Bohr Effect
        • the reason for the bohr effect is linked to how CO2 affects blood pH
        • most of the CO2 from respiring tissues diffuses into red blood cells and is converted to carbonic acid by the enzyme carbonic anhydrase
        • the carbonic acid splits up to give hydrogen ions and hydrogencarbonate ions


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