Outline the four levels of protein structure.

Primary structure is the number as well as the sequence/order of amino acids in a polypeptideSecondary structures are regularly repeating structures which can either be beta-pleated sheets or alpha-helices held together by H-bondsTertiary structure is the 3-dimensional structure of the polypeptide held by bonds such as but not limited to ionic bonds, H-bonds, hydrophobic interactions, disulfide bridges or interactions between R groupsQuaternary structure links two or more polypeptides to form one protein