Haemoglobin. Computer model of the haemoglobin molecule that transports oxygen around the body in red blood cells. It has four iron-containing haem groups (coloured spheres). The rest of the haemoglobin structure consists of four globin proteins (amino acid chains, coils). Each globin protein is wrapped around a haem group, protecting it from being oxidised and destroyed by the oxygen it is intended to transport. The structure of the haem molecules is not clearly seen, but the atoms are colour-coded: carbon (yellow), oxygen (red), nitrogen (blue) and iron (green). It is this iron atom that reversibly bonds to oxygen and carbon dioxide in the blood.