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.
- 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…