Lecture 3b Flashcards
(25 cards)
At the end of the gene, specific sequences when transcribed into RNA trigger what?
Transfer of enzymes to RNA
What are the 2 cleavage factors?
CstF and CPSF
What is PAP and PABP
Poly A Polymerase
Poly A Binding Protein
What happens once message is cleaved?
Poly A Tail is added and transcription is terminated
What is further extended in the last phase?
Poly A tail is extended and is important for mRNA stability and function
What are the 3 differences between transcription between prokaryotes and eukaryotes
Chromatin (no nucleosomes in pro)
3 RNA polymerases (1 in pro)
RNA processing (pre-mRNA in euks and not in Pros)
3 steps for pre-mRNA to mature mRNA
- Addition of a 5’ cap
- Addition of polyA tail
- Removal of introns
What is added to the 5’ end of pre-mRNA while still being transcribed and what enzyme is used to add this?
Guanyl transferase adds guanine nucleotide to the 5’ end
When is 5’ capping initiated?
Once 20-30 nucleotides have been transcribed
What is one reason the 5’ cap is needed
Required for translation initiation in euks
Poly-A sequence is added by what and is important for what?
Poly A polymerase, PAP. For mRNA stability.
The pre-mRNA contains what that signal the beginning and end of introns?
Consensus nucleotide sequences
What are snRNAs
Small nuclear RNA molecules that are in the spliceosome
snRNAs associate with other proteins to form what?
snRNPs
What forms the spliceosome complex?
snRNPs
why does intron splicing need to be precise?
Errors in splicing affects the reading frame for translation
What is tRNA?
Highly stable RNA molecule which is the adapter molecule between the mRNA and peptide sequences
What enzyme attaches the amino acid to the respective tRNA
Aminoacyl tRNA synthetase (aaRS)
What are the 3 sites in the large ribsomal subunits?
E site, P site, A site
exit, peptidyl, aminoacyl
Describe initiation of translation?
Euk initiation factors (eIF) associate with 5’7mG cap of mRNA, 40S ribosomal subunit and Met tRNA.
This complex searches for AUG codon to start.
Large ribosomal subunit (60S) then binds.
80S initiation complex is then formed
Describe elongation translation
Met is the first amino acid, and this tRNA is in the P site.
The next tRNA sits in the A sire and the Met amino acid forms a peptide bond with the Amino Acid in the A site and the old tRNA moves onto the E site and exits
Describe translation termination
Elongation occurs till a stop codon is encountered.
A release factor binds to the A site instead of a tRNA which prompts termination.
mRNA sequence is decoded in sets of what?
3 nucleotides
What makes a charged tRNA?
A tRNA with the respective amino acid attached
