Describe the structures of proteins.

Proteins are made up of the primary structure, secondary structure and tertiary structure. Some proteins may also have a quaternary structure. The primary structure is the specific sequence of amino acids, peptide bonds join the amino acids together. The secondary structure is the folding is the primary structure into alpha helices and beta pleated sheets, these have peptide bonds, hydrogen bonds, ionic bonds and disulphide bridges. The tertiary structure is folding of the secondary structure into a 3D shape with peptide bonds, hydrogen bonds, ionic bonds, disulphide bridges and hydrophobic and hydrophilic interactions. The quaternary structure belongs to proteins with 2 or more peptide chains, they sometimes have a prosthetic group.