Posttranslational modification means the
chemical modification of a
protein after its
translation. It is one of the possible steps in
protein biosynthesis.
A protein is a chain composed of 20 possible amino acids (also called polypeptide). Some posttranslational modification extends the range of possible functions a protein can have by introducing other chemical groups into the makeup of a protein (e.g., carbohydrate chains). Other modifications like phosphorylation are part of common mechanisms for controlling the behavior of a protein.
Types of posttranslational modifications include:
- phosphorylation, the addition of a phosphate group, usual to serine, tyrosine, threonine or histidine
- acetylation[?], the addition of an acetyl group, usually at the N-terminus[?] of the protein
- farnesylation[?], the addition of a farnesyl[?] group
- glycosylation[?], the addition of a glycosyl[?] group to either asparagine, hydroxylysine, serine, or threonine, resulting in a glycoprotein