Haemoglobin - BIOL2 AS

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Structure of a haemoglobin molecule: 

  • Primary structure - 4 polypeptide chains
  • Secondary structure - each polypeptide chain coiled into a helix
  • Tertiary structure - polypeptide chains folded into a precise chape - important factor in the ability to carry oxygen. 
  • Quaternary structure - all 4 chains linked to form an almost spherical molecule. Each polypeptide is associated with a haem group, containing a ferrous ion (Fe2+) each Fe2+ ion can combine with a single oxygen molecule meaning 4 O2 molecules can be carried by a haemoglobin molecule.

Role of Haemoglobin: Transporting Oxygen:

  • It must readily associate with oxygen at the surface where gas exchange takes place.
  • it must readily dissociate from oxygen at those tissues requiring it. 

Different Haemoglobins: 

  • Haemoglobins with a high affinity for oxygen - these take up oxygen more easily but release it less readily
  • Haemoglobins with a low affinity for oxygen - these take up oxygen less easily but release it more readily

Associating with oxygen occurs in the lungs and dissociating occurs in the tissues.

Oxygen Dissociation Curves: 

At low concentrations of oxygen, the polypeptides are closely united, making it difficult to…


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