Haemoglobin and Bohr effect

Cards (16)

  • Haemoglobin
    • Has four polypeptide chains
    • Each polypeptide chain contains a haem group
    • Each of the four haem groups combined to one oxygen molecule
    • 1 molecule of haemoglobin combined to a maximum of four oxygen molecules
  • Oxygen dissociation curve
    Plot of percentage saturation of haemoglobin with oxygen against the partial pressure of oxygen
  • Affinity of haemoglobin for oxygen
    How strongly haemoglobin binds to oxygen, depends on the partial pressure of oxygen
  • In the alveoli, the partial pressure of oxygen is high
  • Under high oxygen partial pressure in alveoli, haemoglobin has a high affinity for oxygen and has an oxygen saturation of around 97%
  • Almost all of the haemoglobin molecules have loaded 4 oxygen molecules under high oxygen partial pressure
  • As red blood cells move from lungs to tissues

    1. Partial pressure of oxygen decreases
    2. Tissue cells take up oxygen for aerobic respiration
  • At a certain partial pressure, an average of 1 oxygen molecule now unloads from each haemoglobin molecule
  • Unloading of oxygen
    • Changes the quaternary structure of haemoglobin
    • Reduces the affinity of the haem groups for oxygen
  • In very active tissue, the partial pressure of oxygen falls even further because the haemoglobin has reduced affinity for oxygen, making it easier for more oxygen molecules to unload
  • Bohr effect
    • Increased carbon dioxide partial pressure shifts the oxygen dissociation curve to the right
    • Reduces the oxygen affinity of haemoglobin
  • Low carbon dioxide partial pressure

    Haemoglobin 75% saturated at 7 kPa oxygen partial pressure
  • High carbon dioxide partial pressure
    Haemoglobin only 25% saturated at 7 kPa oxygen partial pressure
  • In the lungs, haemoglobin has a high affinity for oxygen due to low carbon dioxide partial pressure so has a high level of oxygen saturation
  • In active tissues undergoing aerobic respiration with high carbon dioxide partial pressure, haemoglobin has lower oxygen affinity so more likely to unload oxygen
  • Carbon dioxide forms carbonic acid in blood
    1. Carbonic acid releases hydrogen ion H+
    2. Carbonic acid combines with haemoglobin
    3. Changes haemoglobin quaternary structure
    4. Reduces haemoglobin's affinity for oxygen
    5. Causes haemoglobin to unload oxygen more easily