Main Body
Eukaryotic Translation-Elongation & Termination
Eukaryotic Translation-Elongation & Termination
Dr.V.Malathi
The sequence of steps in the process of elongation are :
•Movement of ribosome to next codon
•Incoming aminoacyl tRNA brought to the ribosome by eEF-1α- GTP.
•GTP hydrolysed
•eEF-1α- GDP- complex dissociates
•GDP/ GTP exchange for additional translocations.( carried out by eEF-1 βγ).
•Peptide in ribosome P-site transferred to aminoacyl-tRNA in A site.
•Reaction called Transpeptidation ; catalysed by peptidyl transferase.
•Peptidyl tRNA movement from A site to P site called –Translocation. Catalyzed by eEF-2: coupled to GTP hydrolysis
•In the process of translocation- Ribosome moved to next codon of mRNA resides in the A site.
•eEF-2 released. Cycle begins again.
Regulation
•Ability of eEF-2 to carry out translocation is regulated by state of Phosphorylation
•When phosphorylated enzyme is inhibited
•Phosphorylation catalyzed by eEF2Kinase (eEF2K).
•eEF2K activated by calcium.
•Phosphorylation of eEF2K by mTOR- master metabolic regulatory Kinase – inactivates eEF2K
Termination
•Requires releasing factors – eRFs
•Termination signal – UAG, UAA and UGA
•eRF binds to A site along with GTP
•This binding stimulates peptidyl transferase activity to transfer the peptidyl group to water
•Uncharged t RNA left in p site expelled with GTP hydolysis
•80S complex dissociates