Translation (Part-II)

POST TRANSLATIONAL MODIFICATIONS: Post Translational modifications are chemical modifications which play a critical role in functional proteomics, because it regulate  position, activity and interaction with other cellular molecules like proteins, lipids, nucleic acids, and cofactors  etc. Post Translational modifications occur at different amino acids side chains or  at peptide linkages and is carried out by different enzymes  like phosphatases, kinases, transferases and ligases which main function are mainly addition or removal of different functional groups or sugars to or from amino acids side chain. And it also involves the proteases, which main function is to cleave peptide bonds or to remove specific sequences or regulatory subunits from a large polypeptide.
Post Translational modification is not a rapid process, but it can occur at any step in protein life cycle, Some proteins are modified soon after translation because it require proper protein folding of nascent protein for stability. Some other modifications occur after folding and localization to activate or inactivate catalytic activity or to stimulate the biological activity of the protein. Proteins are also linked covalently with the tags that target a protein.
Protein Post Translational modifications can also be reversible or irreversible, it basically depend upon the nature of the protein modification. Example, kinase phosphorylate side chains of specific amino acid of any protein, it is a very common method of protein activation or inactivation.  Phosphatases hydrolyze the phosphate group to remove it from the side chain of specific amino acids of a protein and reverse the biological activity against the kinases.