Molecular computer graphics of a 2-zinc insulin hormone molecule, (a hexamer). The molecule is made up of two chains of amino acids: the A chain, two small cylinders of the same colour (yellow & green), & the B chain, one large cylinder (blue). The chains are held together by two sulphur bonds (ribbons), with the zinc atoms (white balls) at centre. Insulin is produced in the pancreas by the 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, or diabetes.