23. The polypeptide chain is elongated via a repeating three-step reactions The next aminoacyl-trNa is delivered to the a (aminoacyl) site of the ribosome by EF-Tu-GTP(step 1) EF-Tu(being about 5%of the total bacterial protein)is believed to protect the activated ester bond from being hydrolyzed by water The milliseconds taken for gTP hydrolysis on EF-tu and milliseconds for ef- tu-gdp to leave is believed to allow the anticodon-codon interaction to be proofread The fMet group is transferred to the second aminoacyl trNa in the a site to form a peptide bond, generating a dipeptidyl-tRNa(step 2
23. The polypeptide chain is elongated via a repeating three-step reactions • The next aminoacyl-tRNA is delivered to the A (aminoacyl) site of the ribosome by EF-Tu-GTP (step 1). • EF-Tu (being about 5% of the total bacterial protein) is believed to protect the activated ester bond from being hydrolyzed by water. • The milliseconds taken for GTP hydrolysis on EF-Tu and milliseconds for EF-Tu-GDP to leave is believed to allow the anticodon-codon interaction to be proofread. • The fMet group is transferred to the second aminoacyltRNA in the A site to form a peptide bond, generating a dipeptidyl-tRNA (step 2)
The 23S rRNA of the large subunit of the ribosome seems to have the peptidyl transferase activity. thus being a ribozyme(noller, 1992) EF-G(the translocase) then promotes the translocation of the ribosome along the mrna by the distance of one codon: the deacylated tRNAtMet s released from the e (exit) site of the ribosome, the dipeptidyl-trNa is relocated to the P site, and the a site is open for the incoming(the third) aminoacyl- tRNa (step 3)
• The 23S rRNA of the large subunit of the ribosome seems to have the peptidyl transferase activity, thus being a ribozyme (Noller, 1992). • EF-G (the translocase) then promotes the translocation of the ribosome along the mRNA by the distance of one codon: the deacylated tRNAfMet is released from the E (exit) site of the ribosome, the dipeptidyl-tRNA is relocated to the P site, and the A site is open for the incoming (the third) aminoacyltRNA (step 3)
Initiation E site P site A site Step 2: peptide Polypeptide bone ormation E UAC 23S rRNA)chain is s Deacylated elongated on :9 Dsa the ribosome GTP E site A site ↓Step3 Translocate Step 1 (EF-G) Aminoacyl Incoming tRNAenters Onc aminoacyl-tRNA the a site NH EF-T R-C-H A UG P A Direction of bosome movement
AA2 Polypeptide chain is elongated on the ribosome Step 1: AminoacyltRNA enters the A site (EF-Tu) Step 2: peptide bond formation (23S rRNA) Step 3: Translocation (EF-G)
The ef-Tu-gTP F aminoacyl-tRNA Ffu complex AminoieyFRN EF-G has a structure similar to EF-Tu-tRNA
The EF-Tu-GTPaminoacyl-tRNA EF-Tu complex Aminoacyl-tRNA EF-G has a structure similar to EF-Tu-tRNA