The Role of Haemoglobin

• Haemoglobin


  Protein in red blood cells that transports the majority of oxygen around the body
• Red blood cells (erythrocytes)

  • Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen
  • Each molecule of haemoglobin can carry four oxygen molecules, or eight oxygen atoms in total
  • Each red blood cell contains about 280 million haemoglobin molecules
• Oxygen transport


  1. Oxygen binds to haemoglobin to form oxyhaemoglobin

  2. Binding of first oxygen molecule results in conformational change making it easier for each successive oxygen molecule to bind (cooperative binding)

  3. Reverse process happens when oxygen dissociates in the tissues
• Carbon dioxide transport


  1. Carbon dioxide dissolves directly in blood plasma

  2. Carbon dioxide binds to haemoglobin forming carbaminohaemoglobin

  3. Majority of carbon dioxide transported as hydrogen carbonate ions (HCO3-)
• Formation of hydrogen carbonate ions


  1. Carbon dioxide diffuses into red blood cells

  2. Carbonic anhydrase enzyme catalyses reaction between carbon dioxide and water to form carbonic acid (H2CO3)

  3. Carbonic acid dissociates into hydrogen carbonate ions and hydrogen ions

  4. Haemoglobin acts as a buffer by accepting hydrogen ions to form haemoglobinic acid
• Chloride shift


  1. Hydrogen carbonate ions formed are transported out of red blood cells

  2. To maintain electrical balance, chloride ions are transported into red blood cells via the same transport protein