Module 4 Section 5 Flashcards
1
Q
Elongation: delivery of charged tRNA to prokaryotic decoding center steps
A
- Charged tRNA delivered to A-site by EF-Tu-GTP (elongation factor thermo unstable)
- A1492 and A1493 (adenosine) ‘flip out’ in response to the correct codon-anticodon BP
- causes conformational changes to the 30S subunit
- EF-Tu-GTP hydrolyzed to EF-Tu-GDP
- tRNA rotates into position (accomodation)
EF-Tu is eEF1alpha in eukaryotes
2
Q
Elongation: Peptidyl transferase rxn
A
- peptide bond is formed between 2 AA bound by their tRNAs to the A and P sites on the ribosome
1. alpha-amino group of amino-acyl tRNA in the A site attacks the carbonyl carbon of the ester bond linking the peptide to the tRNA in the P-site - alpha-amino is nucleophile
2. growing chain is transferred to the tRNA in the A site - as ribosome shifts along mRNA, uncharged tRNA now moves to the E site and the peptidyl-tRNA moves to the P-site
- this frees A site to bind next tRNA
- peptidyl transferase is the enzyme that catalyzes the peptide bond formation
3
Q
Aminoglyceride antibiotics
A
- cause inappropriate flipping of the A1492/3 for non-cognate tRNAs
- used to kill bacteria through translational fidelity (misfolded proteins = death)
- at high doses, can cause read through of nonsense mutations in eukaryotes
4
Q
Puromycin antibiotic
A
- inhibitory antibiotic
- structure is very similar to the 3’ end of an aminoacyl-tRNA
- fits into peptidyl transferase center
- not bound to the ribosome by interactions with 16S rRNA
- if bound to chain, the peptide dissociates b’c the puromycin is not bound to the ribosome