Haemoglobin: structure and function

• red blood cells:

  • biconcave shape gives large SA : V for diffusion of oxygen
  • flat and thin which creates a short diffusion pathway for oxygen
• haemoglobin is a large globular protein with quaternary structure. each chain has a haem group which contains an iron ion
• oxygen associates into the haem from the lungs to form oxyhaemoglobin. Can also be reversed and the oxygen can be dissociated. Also known as loading and unloading oxygen
• Haemoglobins affinity for oxygen:

  • partial pressure of oxygen
  • haemoglobin saturation
  • the partial pressure of carbon dioxide
• the partial pressure of a gas is a measure of concentration of that gas in a mixture. So the higher the concentration of oxygen the higher the pO2 and as pO2 increases haemoglobins affinty increases
• haemoglobin will have a higher affinity for O2 in oxygen rich areas where there is a high pO2 promoting oxygen loading
• haemoglobin will have a lower affinity for O2 in oxygen starved areas where there is a low pO2 promoting oxygen unloading
• as one oxygen binds to the haemoglobin, it changes the haemoglobin shape making it easier for the next oxygen to bind