Insulin is a protein hormone whose primary functions are:
*To enable glucose to be transported across cell membranes
*To convert glucose into glycogen for storage in the liver and muscle
*To aid the conversion of excess glucose to fat
*To prevent the breakdown of protein for energy.
The hormone is a 51-residue anabolic protein that is secreted by the β-cells in the Islets of Langerhans. Insulin is stored in the pancreas as hexamers, ready to be released in response to external stimuli.
Proteins are polymer chains of amino acid residues. Each number on the model represents one amino acid residue. Some sections of amino acid chains curl and form α-helices due to hydrogen bonds between N-H and C-O groups.
The insulin molecule consists of two polypeptide chains, the A chain (21 amino acid residues) and B chains (30 residues), linked by two disulphide bridges.
A disulfide bridge is formed when a sulphur atom from the residue cysteine forms a single covalent bond with a sulphur atom from a second cysteine.
Structure of insulin
