translation Flashcards
What RNA does translation occur in?
mRNA
Ribosomes
enzymes (ribozymes) that perform protein translation. The ribosome contains protein and rRNA components
consists of large and small subunit (which are each comprised of rRNA and proteins)
What are the 3 sites on the ribosome for tRNA binding?
Exit site: uncharged tRNAs exit at this site
Peptidyl site: growing peptide chain is found on the tRNA
Aminoacyl cite: charged tRNAs enter at this site
3 phases of translation (with the goals)
Initiation
Goal: load on the ribosome onto the mRNA
Elongation
Goal: build a peptide chain
Termination
Goal:stop protein synthesis, disaemmble the ribosome
Shine-Dalgarno sequence
16s rRNA binds to ribosome binding site
UAAGGAGGU
Initation factors
small proteins that aid in ribosome assembly
What is at the end of initation?
All together, this is the 70S subunit
The ribosome is assembled on the mRNA and the first tRNA is attached to the initation codon in the P site of the ribosome
tRNAs in prokaryotes
Short RNAs that bring amino acids to the ribosome
Carries a special amino acid, called f-met
How is charged tRNA delievered to the A-site of the ribosome?
By the elongation factor (EF-Tu) + energy. Additional EFs are also involved.
EFs are then released (and can be reused)
translation elongation
The amino acid on P-site tRNA is attached to the amino acid on the A-site tRNA (to create the first peptide bond)
The ribosome moves downstream to shift the uncharged P-site tRNa to the E-site, where it is released.
The tRNA with the peptide chain is now in the P site
A new charged tRNA is recruited to the A site and this process repeats
Release factor (termination)
recruited to the stop codon. This causes the ribosome to disassemble and fall off the mRNA and the protein chain to be released
Operons
Only found in prokaryotes
Cluster of ORFs (genes) that are transcribed together on one mRNA (one promoter/terminator)
polycistronic mRNAs
Containg more than one ORF
Where does translation and transcription occur in eukaryotes?
translation –> cytosol
transcription –> nucleus
transcription and translation are not coupled!
While in prokaryotes they occur simultaneously
Exons
sequences that are translate d intro proteins
Introns
Sequences flanked by exons must be spliced out prior to translation
Where does splicing of introns occur?
nucleus
Ribosome binding site overlaps the start codon:
Kozak sequence (AUG)
What are at the end of eukaryotic mRNAs
Poly-A tail
Eukaryotic translation: initation
the ribosome is recruited to euk. mRNAs with the help of initiation factors called CAP-bidning proteins that bind to the 5’ and 3’ polyA tails of the mRNA.
What is the initation complex in eukaryotic translation called?
CAP complex
What to tRNAs carry in eukaryotic translation?
carries met
Who are faster at making proteins?
Prokaryotes
