Haemoglobin & Oxygen (AQA AS Biology): Revision Note

Haemoglobin

• Haemoglobin is a protein that belongs to a group of chemically similar molecules found in many different organisms

• Haemoglobin has a quaternary structure that consists of four polypeptide chains

  • It has two α–globins and two β–globins

  • The four globin subunits are held together by disulphide bonds

  • Hydrophobic R groups face inwards, helping to preserve the spherical tertiary structure

  • Hydrophilic R groups face outwards, helping to maintain solubility

• Each chain, or subunit, contains a haem group which is able to reversibly combine with an oxygen molecule

  • The haem group contains an iron II ion (Fe²⁺) 

  • Each haemoglobin can therefore transport four oxygen molecules (O₂)