Describe the structure of a protein

All proteins are polymers of amino acids arranged with varying degrees of complexity. The most basic structure is the order of amino acids, this is called the primary structure. Amino acids form peptide bonds between the carboxyl group on one amino acid, and the amino group on another, to create chains called polypeptides. This is a condensation reaction, meaning a molecule of water is formed. The secondary structure is the folding of a polypeptide chain into an alpha-helix or beta-pleated sheet, this is held in place by hydrogen bonds. The tertiary structure is further folding to create a 3-D shape which is secured by hydrogen bonds, ionic bonds and disulphide bonds between R groups. The quaternary structure is formed when two or more polypeptide chains create an extremely complicated but specific shape, for example haemoglobin which is formed from four polypeptide chains and an inorganic iron group.