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  • Created by: tiacoles
  • Created on: 29-02-16 20:17

Haemoglobin and Oxyhaemoglobin

  • Human haemoglobin is found in red blood cells - it carries oxygen around the body. 
  • It is a large protein with a quaternary structure - it has four polypeptide chains. Each chain has a haem group which contains iron and gives it it's red colour. 
  • Each molecule can carry four oxygen molecules. 
  • In the lungs, oxygen joins to the iron to form oxyhaemoglobin. 
  • This is a reversible reaction. 
  • When an oxygen molecule joins it is known as association or loading. and when it leaves it is dissociation or unloading. 

Affinity for Oxygen and pO2

  • Affinity means the tendency a molecule has to bind. 
  • The affinity varies depending on the conditions - one being the partial pressure of oxygen (pO2)
  • This is a measure of oxygen concentration. 
  • The greater the concentration of dissolved oxygen in cells, the higher the partial pressure. 
  • As pO2 increases, haemoglobin's affinity for oxygen increases:
  • Oxygen loads onto haemoglobin to form oxyhaemoglobin when there's high pO2. 
  • Oxygen enters blood capillaries at the alveoli in the lungs. 
  • Alveoli have a high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin. 
  • When cells respire, they use up oxygen - lowering pO2.
  • Red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads its oxygen.
  • The haemoglobin then returns to the lungs to pick up more oxygen. 

Dissociation Curves

  • Shows how saturated the haemoglobin is with oxygen at any given partial pressure. 
  • The affinity of haemoglobin affects its saturation. 
  • Where partial pressure is high, haemoglobin has a high affinity


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