Protein Bonding

Three (plus one further interaction) main types of chemical bonding hold a protein's folded structure together. Hydrogen bonds form between certain hydrogen atoms and the oxygen or nitrogen atoms of the polypeptide backbone: the hydrogen atoms carry a small positive charge while the oxygen/nitrogen atoms carry a small negative charge, so opposite charges attract and form a bond. Individually these bonds are weak, but because so many of them form throughout a folded protein, together they help maintain its overall 3D shape. Ionic bonds form between charged groups on the protein that are not otherwise linked by a peptide bond; these are stronger than hydrogen bonds but can still be broken by changes in pH or temperature. Disulfide bonds form specifically between the sulphur atoms of amino acids that contain sulphur, such as cysteine and methionine, creating a strong covalent 'bridge' between two parts of the chain - the more distant the linked sulphur atoms are along the chain, the more the protein bends at that point (this is literally the chemistry behind curly hair: more distant disulfide bridges between keratin strands make the hair curl more). Hydrophobic interactions additionally help …