Prokaryotic Translation Flashcards
What are the main steps involved in prokaryotic translation?
Initiation
Elongation
Termination
In which direction is mRNA translated?
5’ to 3’
What is initiation?
Steps that are taken before polypeptide chain formation
This is done through IFs. (Initiation factor)
Elongation?
Addition of amino acids to the polypeptide chain through elongation factors
Termination?
Stopping of protein synthesis through release factors
Which specific codon does protein synthesis start at in an mRNA strand in prokaryotes?
AUG
What is the purpose of the Shine-Dalgarno sequence?
Sequence of bases that bind to the small subunit of a ribosome.
Where does tRNA bind?
On the AUG codon
What is the 30S subunit?
Small subunit of ribosome.
Special type of tRNA initially binds to start to AUG.
Methionine tRNA.
When does the large subunit of ribosome (50S) bind to the mRNA?
After tRNA binds to AUG codon.
GTP is hydrolysed for this reaction to occur.
Where does the next tRNA molcule bind to the initial tRNA?
The empty A site.
Again GTP is hydrolysed
How are peptide bond formed between adjacent AAs on the ribosome?
Bond between P site tRNA and AA broken.
Enzyme (Peptidyl transferase) formed peptide bond.
What occurs in translocation?
Ribosome shifts to the right to give an empty A site.
Does the uncharged tRNA leave the E site?
Yes, but only after translocation of the ribosome.
When does the elongation cycle come to a finish?
When a stop codon is encountered.
What recognises the stop codons?
Release factors, not the charged tRNAs.
Purpose of RF1/2?
Protein that binds to stop codon on the mRNA strand.
What does the binding of RF1/2 trigger?
Enzuyme to cleave off the AA chain from the tRNA molecule
Purpose of Ribosome recycling factor (RRF)?
Binds to A site of ribosome after release of RF1/2
Release of GTP translocates RRF to P site as tRNA translocates to the E site.
RRF releases and disassembles the ribosomal complex.
Role of polyribosome?
Number of ribosomes translating same mRNA strand sequentially
How is the Ef-Tu-GTP recycled after binding of tRNA to the A site?
- GDP displaced by Ts
- Ts displaced by GTP
- Regeneration of EF-Tu-GTP complex is complete
- New tRNA can bind to it
Where is the E, P and A site located on a ribosome?
E behind, P present, A after
What are the three termination codons?
UAA
UAG
UGA
