-Primary structure is the number and sequence of amino acids in a polypeptide.-The secondary structure of a polypeptide is the formation of alpha helices and beta- pleated sheets stabilised by hydrogen bonding. -The tertiary structure is the three-dimensional conformation of a polypeptide, stabilised by intramolecular bonds and interactions between amino acids in the polypeptide. examples of these interactions include disulphide bridges, ionic bonds, and hydrophobic interactions. -The quaternary structure of a polypeptide is the linking of two or more polypeptides to form a single protein.