Genetics 6 Sections19 LessonsLifetime
Post Translational Modifications
Post Translational Modifications
- Many polypeptide chains are covalently modified.
- These are modified either while they are still attached to the ribosome, known as Cotranslational modifications, or
- After their synthesis has been completed. These are called Posttranslational modifications,
- These modifications may include removal of part of the translated sequence or
- The covalent addition of one or more chemical groups required for protein activity.
- These modifications are:
Trimming
Covalent attachments
Protein folding
Protein degradation.
1. Trimming
- The Precursor molecules (Proteins that are synthe4sized) are not functionally active.
- Some portions or parts of the protein chain must be removed.
- This function is carried out by specialized known as Endoproteases.
- This removal of a part from the chain results in the release of an active molecule.
- For example Insulin, Angiotensin.
2. Covalent Attachments
- The newly formed Proteins may be activated or inactivated by the covalent attachment of a variety of chemical groups.
- These include:
- Phosphorylation: Phosphorylation occurs on the hydroxyl groups of serine; threonine; or, less frequently, tyrosine residues.
- Glycosylations: almost all proteins in the body are glycosylated except 3 types of proteins.
- Hydroxylations: also occurs in various proteins.
- Other
3. Protein Folding
- Proteins after synthesis, must fold to assume their functional, native state.
- Folding can be spontaneous (as a result of the primary structure) or
- Facilitated by proteins known as chaperones.
4. Protein Degradation
- Proteins that are defective (for example, misfolded) or destined for rapid turnover are often marked for destruction by Ubiquitination
- Ubiquitination is the attachment of chains of a small, highly conserved protein, called Ubiquitin.
- The proteins that are marked by Ubiquitin are directed to the Proteosomes where they are degraded.