Protein folding is the process by which a large sequence of amino acids is arranged physically into the complex structure of a functioning protein. Proteins are chains of amino acids. They are synthesized from an mRNA template during a cellular process known as translation. Even while the chain is still being formed, it typically begins to re-orient itself. For instance, hydrogen bonds may form between amino acids on different segments of the chain. Sections with polar chemical groups will tend toward the outside of the protein, while groups with hydrophobic side chains are often found in the centre of the macromolecule where they are less likely to interact with water. Protein folding is highly dependent on the external factors such as the solvent, concentration of salts, and temperature. In some cases, additional proteins called chaperones are required to mediate the folding process, ensuring that the correct structure is formed.
The three-dimensional structure of proteins is what gives them their utility. Proteins function as enzymes which catalyze desirable chemical reactions, are integral structural components of the cell, and provide biochemical signals and receptors for the cell. As a result, proteins drive many of the reactions and processes which are vital to the life of the cell.
Improper folding of proteins may cause serious diseases. One famous example which affects humans is Creutzfeldt-Jakob disease (CJD). The mis-folded prion protein forms protein aggregates in cells, and is able to cause healthy versions of the protein to become mis-folded as well. This causes the disease to spread quickly, disrupting cell function.