Module 04 - Section 05 Flashcards
Translation Elongation and Termination in Prokaryotes and eukaryotes
During the elongation phase of translation, what are the 3 steps to add each amino acid?
(1) binding of aminoacyl-tRNA in the A site
(2) Peptide bond formation between the polypeptide in the P site and the amino acid in the A site, transferring the growing polypeptide chain to the tRNA in the A site
(3) Translocation, or shifting of the tRNAs and mRNA by one codon
What are the 4 steps of the delivery of charged tRNAs to the prokaryotic decoding center?
(1) EF-Tu-GTP delivers a charged tRNA to the A-site of an active ribosome at the decoding center of the ribosomal complex and 2 adenosine residue “flip out” in response to the correct codon-anticodon base pairing
(2) Energy is provided by the hydrolysis of EF-Tu-GTP to EF-Tu-GDP+Pi
(3) Correct codon-anticodon pairing causes change in ribosomal configuration, process known as accommodation + release of EF-Tu-GDP (wrong pairing causes dissociation of charged tRNAs from A site)
(4) EF-Tu-GDP is recycled to EF-Tu-GTP through the action of EF-Ts
What are the 3 steps in the peptidyl transferase reaction in prokaryotes?
(1) Formation of first peptide bond occurs through the transfer of the initiating N-formylmethionyl group from its tRNA in the P site to the amino group of the aminoacid in the A site
(2) A nucleophilic attack of the alpha amino group of the A site aminoacyl-tRNA ON the carbonyl carbon of the ester bond linking the fMet to the P-site tRNA forms the peptide bond
(3) Growing chaing is transferred to the tRNA in the A site, now uncharged tRNA moves to the E site and peptidyl-tRNA to the P site
What is the primary target of many naturally occurring antibiotics and toxins?
Protein synthesis
Name two classes of antibiotics that interfere with translational elongation in bacteria
(1) aminoglycosides
(2) Aminonucleosides
How do aminoglycosides interfere with translational elongation?
They bind specifically to the decoding center of the small ribosomal unit and cause inappropriate flipping of A1492/A1493 even when incorrect tRNA is positioned in the A site
– they kill bacteria through errors in translational fidelity by causing misfolded proteins
What are 3 examples of aminoglycosides?
Gentamicin, Streptomycin, Paromomycin
How do aminonucleosides interfere with translational elongation?
They bind to the ribosomal A site and participate in peptide bond formation and then the growing polypeptide is transferred to them. They then dissociate from the ribosome causing the protein to prematurely stops elongation
Name an example of an aminonucleoside
Puromycin
What is required for termination?
Release Factors (RFs)
What are the primary RFs factor in
A) prokaryote
B) eukaryote
a) RF-1, RF-2
b) eRF1
How are release factors involved in the termination of translation?
They recognize termination codon and bind the A-site of the ribosome similarly to tRNA
They bind at the stop codon and induces peptidyl transferase to transfer the growing polypeptide to a water molecule
What stop codons does RF-1 recognize?
UAG and UAA
What stop codons does RF-2 recognize?
UGA and UAA
