Insulin. Computer graphic showing a part of the molecule of human insulin. A single insulin mole- cule is made up of two chains of amino acids, the A and B chains, which are held together by di- sulphide bridges. Here, a detail of the B chain is seen. Atoms are spherical and colour-coded: carbon (green), oxygen (red), hydrogen (blue). Atomic bonds drawn as lines show the skeleton of this part of the molecule. Insulin is a hormone which is produced in the pancreas by cells of the Islets of Langerhans. Its function is to regulate blood sugar levels. Insufficient production of insulin leads to an accumulation of glucose in the blood, causing diabetes mellitus.