Haem group. Blurred molecular graphic of a haem group, the part of the protein haemoglobin that gives blood its red colour. Haemoglobin transports oxygen and carbon dioxide around the body. It consists of four chains of the protein globin, each of which contains a haem group. The atoms, represented as balls and sticks, are colour-coded: iron (red), nitrogen (yellow), carbon (grey) and hydrogen (dark blue). Haem is an iron-containing porphyrin molecule. The flat group of four rings around the iron atom give oxygen and carbon dioxide easy access to the iron, allowing them to bind to it, be carried and finally be released without undergoing any chemical change.