Describe the primary, secondary, tertiary and quaternary structure of proteins.

PrimaryThe amine group of one amino acid reacts with the carboxyl group of another during a condensation reaction to form a peptide bond. The products of this reaction are a dipeptide and a water molecule. (draw diagram of reaction)This reaction is repeated for the addition of more amino acids to form a polypeptide chain.SecondaryThe polypeptide chain can form two different structures through hydrogen bonding between the amino and carboxyl groups. These two structures are the alpha helix and beta pleated sheet (draw structures of both showing hydrogen bonding). TertiaryThe polypeptide chain further folds itself into a 3-D shape, made possible through ionic interactions, disulphide bridges and hydrogen bonding. The different structures of the variable side chain R of an amino acid allow different types of bonding to occur and therefore different 3-dimensional shapes. (draw different types of bonding).QuaternaryMore than one polypeptide chain interacts to form the resultant functional protein. Example: the protein Haemoglobin contains four protein subunits/ polypeptide chains.