Haemoglobin

• Haemoglobins - A group of chemically similar molecules found in many different organisms
• Haemoglobin is a protein with a quaternary structure
• Erythrocytes (red blood cells) have a biconcave shape which gives them a large SA:V for diffusion of oxygen
• Erythrocytes (red blood cells) are flat and thin which creates a short diffusion pathway for oxygen to reach all the haemoglobin inside
• Each chain of haemoglobin has a haem group, which contains an iron ion (Fe2+) which gives haemoglobin its red colour
• Each molecule of haemoglobin can bind up to four oxygen molecules as the oxygen binds to the haem group
• In the lungs oxygen diffuses from the alveoli, into capillaries and into red blood cells where it associates (binds) with the haemoglobin to form oxyhaemoglobin
• Dissociation:

  • When the red blood cells reach the tissues in the body, oxygen dissociates (leaves) from the oxyhaemoglobin and it turns back into haemoglobin
• Haem groups:

  • Each polypeptide chain in a haemoglobin molecule has a haem group
  • A haem group is a prosthetic group that is attached to the protein
  • The haem group contain an iron ion, which makes haemoglobin red
• Loading/association - The process by which haemoglobin binds with oxygen

  • In humans this takes place in the lungs
• Unloading/dissociation - The process by which haemoglobin releases its oxygen

  • When oxygen detaches, or unbinds, from haemoglobin
  • In humans this takes place in the tissues
• Affinity of haemoglobin for oxygen - The ability of haemoglobin to attract, or bind, to oxygen
• Affinity:

  If pO2 is high, haemoglobin has a high affinity for oxygen and oxygen binds to haemoglobin
• Affinity:

  If pO2 is low, haemoglobin has a low affinity for oxygen and oxygen dissociates from haemoglobin
• Haemoglobin is made up as:

  Primary structure - Sequence of amino acids in the four polypeptide chains
• Haemoglobin is made up as:

  Secondary structure - Each of these four polypeptide chains is coiled into a helix
• Haemoglobin is made up as:

  Tertiary structure - Each polypeptide chain is folded into a precise shape

  • (An important factor in its ability to carry oxygen)
• Haemoglobin is made up as:

  Quaternary structure - All four polypeptides are linked together to form an almost spherical molecule
• Haemoglobins with high affinity for oxygen:

  • Take up oxygen more easily
  • Release it less easily
• Haemoglobins with a low affinity for oxygen:

  • Take up oxygen less easily
  • Release it more easily