Flashcards in Translation - lecture 4 Deck (24)
What does aatRNA stand for?
Aminoacyl - transfer RNA (basically tRNA)
What does it mean when tRNA is 'charged'?
Coupled with the correct amino acid
What is aminoacylation?
Covalently attach the correct amino acid to the tRNA ( as specified by the anticodon)
What does aaRSs stand for?
How do aaRSs select the right tRNA to be acylated?
Recognisng specific rTNA identifiers present on the acceptor step and anticodon loop. Highly conserved sequences i.e, G1,G2,G3.
How does the tRNA attach to the ribosome?
Ribosomes select aa-tRNA based only on there codon - anticodon interactions
What ribosomes are made of?
Made of rRNA and ribosomal proteins. have 2 subunits ; large and small. Subunits are not self assembling. combine only in presence of mRNA and aatRNA
What are the 4 steps involved in chain initiation?
- Formation of 43S pre- initiation complex
- formation of the initiation complex
- positioning at the start codon
- association of large subunit
What are the 3 steps of polypeptide synthesis?
1 - chain initiation
2 - chain elongation
3 - chain termination
What does elF stand for?
Mechanism of forming the 43S pre - ignition complex
40S - elF3 already bound with elF1A . Then elF2 binds coupled with tRNA via GTP. elf5 also binds
Binding the 43S complex to the mRNA
elF4 complex binds to the mRNA which causes the poly A tail to bind to this too.
pre- initiation complex binds to the elF4 complex
4E,4G and 4A bind first then 4B binds
Positioning the initiation complex at the start codon
- initiation complex unwinds mRNA using elF4 helicase
-initiation complex stops at the AUG start site
Association of the large subunit (60S)
irreversible GTP hydrolysis mediates the association of the 60S - elF6 to the small subunit by the action of elF5.
Whats happened after setting up the initiation complex?
ribosome formed with a methionine at the P position
First step of chain elongation
aatRNA binding. Binds to the A site on the ribosomes . This is mediated by ef1
Second step of chain elongation
GTP hydrolysis induces conformational change in the ribosome . EF1 dissociates.
Third step of chain elongation
Peptide bond formation. amino acid from P transferred to form peptide bond on the A site
fourth step of chain elongation
GTP hydrolysis moves the tRNAs left , positioning in the E and P sites instead
Termination of the chain
Release factors bind to stop condons.
This induces peptidyl transferase to transfer water instead of aatRNA. Release
What antibiotics inhibit translation in prokaryotes?
streptomycin and chloramphenicol
What antibiotics inhibit translation in eukaryotes
What antibiotics inhibit translation in both prokaryotes and eukaryotes?