What is the structure of a protein?

Proteins are a class of molecules made up of small sub-units called amino acids. Every type of protein has a unique structure. The primary structure of a protein is the type and number of amino acids in the protein and the order in which they are arranged, similar to different coloured beads on a piece of string. This string of amino acids is then folded into the proteins secondary structure. Depending on the protein, its secondary structure can either be classified as an alpha-helix (looks like a spiral) or a beta-pleated sheet (looks like a fan). The secondary structure is then folded again into a globular shape which is known as the protein's tertiary structure. Some proteins stop here however some proteins go further and develop a quaternary structure. This involves multiple globular proteins joining together to form a bigger protein.