Protein structure and organization

A protein is made from a long chain of amino acids, also known as a polypeptide chain, linked via peptide bonds.[46] The higher order structure of a protein depends on the sequence of amino acids which form its primary sequence, as various non-covalent interactions between these amino acids ensure proper protein folding. Proteins have specific amino acid sequences, which all identical proteins share.[47] The twenty different amino acids differ in their side chains, which are relatively large and somewhat polar. These individual amino acids are known as monomers, in the polymer chain known as the protein, which assembles through polymerization.[48]

A protein's secondary structure is created by hydrogen-bond interactions between the amide and carboxyl groups of the amino acid backbone. Secondary structure includes the formation of alpha helices and beta sheets.[46] The tertiary structure is the overall shape of the protein, and is usually driven by the protein's tendency to orient hydrophobic amino acid side chains internally, although hydrogen bonding, ionic interactions and disulfide bonds also help to stabilize proteins in the tertiary state [49] Quaternary structure is the overall combination of polypeptide subunits to form the functional unit. All levels of protein structure are based on the previous level. If there is an error in the primary structure of the protein this will carry to the higher levels.[50]