Describe the structure of proteins

Proteins are polymers (large molecules) of amino acids joined by peptide bonds. They are formed by condensation reactions, meaning water is a by-product of their formation, and there are different levels. Primary structures are simply a string of amino acids, secondary structures have folding in the chain due to hydrogen bonds between molecules (e.g. alpha helix or a beta pleated sheet. Tertiary structures have 3D folding due to multiple different bonds (hydrogen and ionic or disulfuric bonds), and quaternary structures have 2 or more polypeptide chains bound together (e.g. haemoglobin).