Editing Protein biosynthesis (section)

==Protein folding==
{{Further|Protein folding}}[[File:Protein folding figure.png|300px|thumb|alt=three individual polypeptide chains at different levels of folding and a cluster of chains| Shows the process of a polypeptide chain folding from its initial primary structure through to the quaternary structure.]]

Once synthesis of the polypeptide chain is complete, the polypeptide chain folds to adopt a specific structure which enables the protein to carry out its functions. The basic form of [[protein structure]] is known as the [[protein primary structure|primary structure]], which is simply the polypeptide chain i.e. a sequence of covalently bonded amino acids. The primary structure of a protein is encoded by a gene. Therefore, any changes to the sequence of the gene can alter the primary structure of the protein and all subsequent levels of protein structure, ultimately changing the overall structure and function.{{cn|date=April 2023}}

The primary structure of a protein (the polypeptide chain) can then fold or coil to form the secondary structure of the protein. The most common types of secondary structure are known as an [[alpha helix]] or [[beta sheet]], these are small structures produced by hydrogen bonds forming within the polypeptide chain. This secondary structure then folds to produce the tertiary structure of the protein. The tertiary structure is the proteins overall 3D structure which is made of different secondary structures folding together. In the tertiary structure, key protein features e.g. the active site, are folded and formed enabling the protein to function. Finally, some proteins may adopt a complex [[protein quaternary structure|quaternary structure]]. Most proteins are made of a single polypeptide chain, however, some proteins are composed of multiple polypeptide chains (known as subunits) which fold and interact to form the quaternary structure. Hence, the overall protein is a [[multi-subunit complex]] composed of multiple folded, polypeptide chain subunits e.g. [[haemoglobin]].<ref name="Khan proteins 2020">{{Cite web |title=Protein structure: Primary, secondary, tertiary & quaternary (article) |url=https://www.khanacademy.org/science/biology/macromolecules/proteins-and-amino-acids/a/orders-of-protein-structure |access-date=11 March 2020 |website=Khan Academy |language=en}}</ref>