Insulin is a hormone - a chemical messenger - which controls the body's sugar metabolism. Proteins such as this are among nature's most complicated molecules.

Attempts began in the 1930s to decode the structure of insulin by examining the diffraction pattern of X-rays bounced off its atoms. This complex task has been compared to decoding the shape of a tree from the shadows its leaves cast on a wall.

Although Dorothy Hodgkin published her first X-ray photographs of the insulin molecule in 1935, it was not until Fred Sanger had determined the order of the 51 groups of amino acids forming one chain of the protein that she was able to determine its three-dimensional arrangement. The two chains which make up insulin are shown in this model, made around 1967. The larger balls represent zinc atoms which were introduced chemically as a reference to help decode the rest.

Pig insulin has been given to diabetics since the 1920s, but understanding its structure has enabled pharmaceutical companies to produce human-type insulin.

Inv. 1991-286