Explain the four levels of protein structure, indicating the significance of each level

There are four levels to a protein's structure:Firstly, the primary structure which is the sequence of amino acids linked by peptide bonds. This level determines the type/function of the protein by influencing the secondary and tertiary structures.The secondary structure is composed of alpha-helices and beta-pleated sheets which are held together by hydrogen bonds.The tertiary structure determines the overall shape of the polypeptide. For example, on an enzyme the active site is specifically shaped by this tertiary structure.Finally, the quaternary structure links the polypeptides together using the same bonds as in the tertiary structure. A prosthetic group can also be attached to aid the function of the polypeptide. An example of a protein with a quaternary structure is haemoglobin - with 4 polypeptide chains.