Regulation of Gene Expression in Eukaryotes Flashcards
How many RNA polymerases do eukaryotes have?
3
What is the function of RNA polymerase II?
Transcribes DNA to pre-mRNA
Does transcription need a primer to be initiated?
No
What is the function of a promoter in eukaryotes?
Determines the site of transciption initiation and directs binding of RNA polymerase II
What are untranslated regions (UTRs)?
Transcribed non-protein coding sequences at mRNA 5’ and 3’ ends
Where do activators bind?
To distal control elements
What is TBP and what is its purpose?
TATA binding protein, it recruits basal transcription factors which in turn recruit RNA polymerase II
When does a transcription bubble form?
After recruitment of helicase
What is required for RNA polymerase II to recognise and bind to promoters?
Basal trancription factors
What is pre-mRNA made up of?
Introns, exons, and untranslated regions
How many maturation processes does pre-mRNA undergo?
3
What does a splicesome recognise?
gu…ag sequence within pre-mRNA introns
Outline the maturation processes of pre-mRNA
- 5’ met-7G CAP addition
- Pre-mRNA splicing
- 3’ cleavage and polyadenylation
What is the advantage of 5’ to 3’ processing?
Promotes mRNA stability and translational efficiency
What is alternative splicing?
Mutiple mRNAs can be produced from a single gene resulting in multiple protein isoforms and mutiple interactions
How does alternative splicing work?
Joining of different exon combinations (the exons must be sequential)
Where are mature mRNA molecules exported from and to?
From the nucleus, to the cytoplasm
Are transcription and translation linked in eukaryotes?
No
What features of translation are conserved between prokaryotes and eukaryotes?
Codon degeneracy and tRNA charging
What does eIF stand for?
Eukaryotic initiation factor
What does a eukaryotic ribosome dissociate into?
40s and 60s subunits
Do eukaryotes have shine dalgarno sequences?
No
How are the 40s and 60s ribosomal subunits kept separate?
eIF3 and eIF6
Describe the steps involved in the assembly of the pre-initiation complex at the TATA box
- TATA binding protein is recruited and binds to the core promoter
- TBP recruits basal transcription factors
- These in turn recruit RNA polymerase II
- DNA helicase is then recruited and a transcription bubble is formed
Which eIFs are involved in the separation of ribosomal subunits?
eIF3 (binds to 40s subunit) and eIF6 (binds to 60s subunit)
Which subunit is involved in the formation of the pre-initiation complex?
40s subunit
What eIF is met-tRNAi associated with?
eIF2
What form is the met-tRNAi in the pre-initation complex?
GTP form
What eIFs are used to help recruit rRNA to the correct position on 40s ribsomal subunit?
eIF1, eIF1A, and eIF5
In the initial step of initiation; what happens?
The pre-initiation complex binds to methyl CAP-binding complex
What is scanning in the context of initation?
The process by which the pre-initation complex moves along mRNA looking for a start codon
What is a Kozak sequence?
- The sequence which must surround the start codon for a pre-initation complex to recognise the AUG
- AUG must have a purine at a -3 position
- AUG must have a G at a +4 position
What occurs when the pre-initation complex finds an AUG in a Kozak sequence?
- It pauses
- Hydrolyses GTP and GDP to lock it in place
- Allows initation factors around the complex to be released
- This allows the 60s subunit to rejoin the complex
How is the 60s subunit attached to the 40s subunit?
Brought in by eIF-5B•GTP which is hydrolysed when the subunit binds
Which site is the first tRNA put in?
P site
Which eEF is responsible for releasing and recycling eEF-1α•GDP?
eEF-1βγ
What is the first step in translation elongation in eukaryotes?
eEF-1α•GTP brings a charged aa-tRNA to the A site, the eEF is then hydrolysed
What mediates the formation of a peptide bond between the C-terminus of aa in the P site and the N terminus of the aa in the A site?
28s rRNA of the 60s subunit
Which eEF is involved in the repositioning of the tRNAs?
eEF2•GTP
Outline how translational termination in eukaryotes occurs
- Stop codons recruit eRF1 which binds to the A site and is joined by eRF3•GTP
- Hydrolysis occurs to produce eRF3•GDP which causes the peptide chain to be released and the ribosome to dissociate
