Translation of mRNA - Stages of translation
14 important questions on Translation of mRNA - Stages of translation
In one sentence, what happens at each stage of translation?
- Elongation: the ribosome slides along the mRNA (5'-3'), while tRNA's bind to the mRNA at the A site in the ribosome, bringing the appropriate amino acids.
- Termination: when a stop codon is reached, disassembly occurs and the newly made polypeptide is released.
Which molecule recognizes the start codon in the mRNA?
Which type of initiator tRNA is used in bacteria?
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Which three initiation factors are involved in the binding of the ribosomal subunits, mRNA and tRNA^fMet to form the initiation complex in bacteria?
How does initiation in bacteria occur (steps)?
- The mRNA binds to the 30S subunit (Shine-Dalgarno sequence is complementary to a sequence in the 16S subunit);
- IF2 promotes the binding of initiater tRNA to the P site on the ribosome;
- IF1 and IF3 are released, IF2 hydrolyzes its GTP and is released;
- The 50S subunit associates;
- The 70S initiation complex is formed.
What are the differences (4) between bacterial translational initiation and eukaryotic translation initiation?
- The initiater tRNA carries methionine rather than N-formylmethionine in bacteria;
- Eukaryotic mRNA's don't have a Shine-Dalgarno sequence, but eIF4 recognizes the 7-methylguanosine cap and facilitates the binding of the 5' end to the mRNA;
- The ribosome scans along the mRNA in search for the AUG start codon, and when recognizing the start codon, the 60S and 40S subunit associate.
How does the ribosome recognize the start codon, according to Kozak's rules?
- Sometimes it uses the second one. The consensus sequence for optimal start codon recognition is as follows:
A/G C C A U G G
-3 -2 -1 +1 +2 +3 +4
The most important ones are the A/G at -3 and the G at +4
What is the decoding function of the ribosome?
What are the steps of the elongation stage of translation in bacteria?
- Peptidyl transfer: amino acid at the A site binds with polypeptide and the polypeptide is removed from the tRNA at the P site to the tRNA at the A site. This is catalyzed by peptidyl transferase;
- The ribosome moves, translocates, to the next codon. This moves the tRNAs at the P and A sites to the E and P sites;
- The uncharged tRNA exits the E site. At the codon at the empty A site, a charged tRNA binds.
How are the names of the A, P, and E sites logically given?
- The P site contains the peptidyl-tRNA (tRNA with attached peptide);
- At the E site, the uncharged tRNA exits.
What are the differences between the release factors of bacteria and eukaryotes?
- Eukaryotes: eRF1 recognizes all 3 stop codons, eRF3 is also needed.
How does termination occur (steps)?
- RF1 or RF2 binds to A site and RF3 also binds;
- The polypeptide is cleaved from the tRNA in the P site and the tRNA is released as well;
- The ribosomal subunits, mRNA, and release factor dissociate.
Why can transcription and translation of one bacterial protein-coding gene happen at the same time, while a eukaryotic protein-coding gene can't be transcripted and translated at the same time?
How can anitibiotics that interfere with bacterial translation be used without interfering with eukaryotic translation?
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