33 - Translation; Chain Elongation

33 - Translation; Chain Elongation - Translation Chain...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
Translation Learning Objectives • Compare the process of translation elongation in prokaryotes and eukaryotes • Describe the association of peptidyl transferase with the RNA moiety of the ribosome Chain Elongation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Elongation –similar in prokaryotes and eukaryotes after initiation of translation, tRNA i Met is on the P site Elongation of a protein chain has three steps: 1. Amino-acyl-tRNA, couples with Tu-Ts (in prokaryotes) or eEF 1 - eEF 1 b (in eukaryotes) and GTP into ternary complex, binds to A site on ribosome and pairs with codon on mRNA. This is catalyzed by GTP. Ts helps reactivation of Tu. 2. Peptide bond forms between previous AA and new AA - peptidyl transferase reaction - previous AA is transferred/bound to the AA carried by amino-acyl-tRNA which now becomes peptidyl-tRNA; it is still at the A site. Unloaded tRNA is still at the P site.
Background image of page 2
3. Ribosome moves to the another codon, down mRNA chain. Translocation is catalyzed by EF G (Pro) or eEF2 (Eu), using GTP energy. 3 a. With this movement peptydil- tRNA shifts at P site, unloaded tRNA is now at the E site. A site is empty. New amino-acyl-tRNA (ternary complex) binds to A site…
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
•tRNA makes direct contact with both 16S and 23S rRNAs in ribosome •rRNAs are highly conserved (much more then ribosomal proteins) Peptidyl transferase - catalyses the transfer of the growing peptide chain to the incoming activated amino acid (at the aminoacyl t-RNA) and makes peptide bond So, what is peptydyl transferase? Nucleic acid – rRNA(s) or protein ribosomal protein(s)? Experiment (1992): •majority (95%) of proteins removed from the large ribosomal subunit (SDS, proteinase K and phenol), •23S rRNA mixed with analogues of aminoacyl-tRNA and peptidyl-tRNA 80% of peptidyl transferase activity retained •Also: activity blocked by RNase Prokaryotic ribosomes could be defined as ribozymes 23S rRNA from the large ribosomal subunit performs enzymatic reaction Another RNA having catalytic activity :
Background image of page 4
Residue G2252 from the P loop forms close contacts with the CCA-end of the P-site (peptidyl) tRNA, and residue G2553 from the A loop forms close contacts with the CCA-end of the A-site (aminoacyl) tRNA. The results indicate that the tertiary sturcuture of 23SrRNA brings the P loop-bound peptidyl-tRNA into an interaction with bases in the central region. ( Adapted from Green,R.,et al., 1998. Ribosome-catalyzed peptide-bond formation with an A-site substrate covalently linked to 23S ribosomal RNA. Science 280: 286-289. ) 23S rRNA Active center of 23S rRNA
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The peptidyl transferase reaction Energy required for the cycle of peptide bond formation(s): 1 ATP - used by the aminoacyl- tRNA synthetase to make a high- energy acyl bond which binds amino acid to the tRNA. The breakage of this high-energy bond will drive the peptidyl tranferase reaction and create the peptide bond .
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 21

33 - Translation; Chain Elongation - Translation Chain...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online