Mass transport

• Primary structure


  Sequence of amino acids in the four polypeptide chains
• Secondary structure


  Each of these polypeptide chains is coiled into a helix
• Tertiary structure


  Each polypeptide chain is folded into a precise shape - an important factor in its ability to carry oxygen
• Quaternary structure


  All four polypeptides are linked together to form an almost spherical molecule
• Haemoglobin molecule


  • Each polypeptide is associated with a haem group - which contains a ferrous (Fe2+) ion
  • Each Fe2+ ion can combine with a single oxygen molecule (O2)
  • A single haemoglobin molecule in humans can carry a total of four O2 molecules
• Loading and unloading oxygen


  Loading or associating - the process by which haemoglobin binds with oxygen takes place in the lungs in humans.

  Unloading or dissociating - the process by which haemoglobin releases its oxygen takes place in the tissues in humans.
• Role of haemoglobin


  Must:

  • readily associate with oxygen at the surface where gas exchange takes place
  • readily dissociate form oxygen at those tissues requiring it