Describe the structure of a protein

There are four structures of a protein: the primary, secondary and tertiary. Primary is the sequence of amino acids in the protein. The secondary structure is the way the protein is either folded into a pleated sheet or an alpha helix due to the hydrogen bonds that form between the C=O and N-H. The tertiary structure is the overall shape of the protein due to the interactions between the R-groups of the amino acids (including hydrogen bonds, ionic bonds and disulfide bridges (between two specific amino acids called cysteine)). The quaternary structure is the way these tertiary structures join together with each other or with other 'prosthetic groups' (for example joining with iron (II) in haemoglobin).