7.1 - Haemoglobin

• what are hoemoglobins?

  a group of chemically similar molecules

  globular proteins made of 574 amino acids
• structure of haemoglobin

  primary: sequence of amino acids in the 4 polypeptide chains

  secondary: each polypeptide chain folds into a helix - 2 alpha and two beta

  tertiary: each polypeptide is folded into a precise shape - important to carry oxygen

  quaternary: each polypeptide is associated with a haem group that has Fe2+ that combines with oxygen. 4 polypeptides are linked together to form an almost spherical molecule
• loading

  process by which haemoglobin binds with oxygen forming oxyhaemoglobin

  happens in the lungs
• unloading

  process by which haemoglobin releases oxygen

  happens in the tissues
• haemoglobin with high affinity for oxygen

  takes up oxygen easily but releases it less easily
• haemoglobin with low affinity for oxygen

  takes up oxygen less easily but releases it more easily
• what's the role of haemoglobin?

  transport oxygen
• how is haemoglobin efficient for its role?

  readily associates with oxygen at gas exchange surface

  readily dissociates from oxygen at tissues requiring it

  achieved by hoemoglobin changing its affinity for oxygen
• how does haemoglobin change its affinity for oxygen?

  its shape changes under different conditions which causes bonds to break

  depends on partial pressure of oxygen and carbon dioxide
• partial pressure

  proportion of substance (gas) present in a mixture of gases & the pressure it contributes to total pressure

  a measure of concentration
• conditions for high affinity for oxygen

  high partial pressure of oxygen and low of carbon dioxide
• conditions for low affinity for oxygen

  loan partial pressure of oxygen and high of carbon dioxide
• prosthetic group in haemoglobin

  iron
• prosthetic group in hemocyanin

  copper
• haemoglobin in organisms with high metabolic rate

  high oxygen demand so haemoglobin needs to have a lower affinity for oxygen so it unloads more
• haemoglobin in organisms that live in places with little oxygen

  haemoglobin has higher affinity for oxygen so loads more
• Why do different haemoglobins have different affinities for oxygen?

  each species produces haemoglobin with different aminoacid sequence so haemoglobin has a different tertiary & quaternary structure so different oxygen binding properties