Describe the structure of proteins

Proteins have a primary, secondary, tertiary and quaternary structure. The primary structure comprises of the specific sequence of amino acids which are held together by peptide bonds. The secondary structure is the hydrogen bonds which form between sections of the polypeptide when the protein chain is coiled or pleated in alpha helices or beta sheets. The tertiary structure involves the various bonds which form within the molecule to give it a complex and specific 3D shape, these include: ionic bonds, disulfide bridges, hydrogen bonds and hydrophilic/hydrophobic interactions. Finally, the quaternary structure is when two or more polypeptide chains are linked to form a functional protein.