L07 Flashcards
what is the difference between eukaryotic and prokaryotic protein synthesis
prokaryotes: transcription and translation are coupled (in the same space)
eukaryotes: transcription happens in the nucleus. translation happens in the cytoplasm (not coupled)
what steps are involved in the regulation of eukaryotic gene expression
- transcription control
- RNA processing control
- Translation control
- Protein activity control
defects in these cause cause genetic diseases
what happens to pre-mRNA after transcription control?
RNA processing control, where pre-mRNA is modified to form mature mRNA in the nucleus.
what is unique about Cap and poly A tail elements of mRNA
- they are present in eukaryotic mRNA only
- not encoded in the genome.
what steps does pre-mRNA go through
- Capping
- Splicing
- Polyadenylation
- editing
These events are coupled to transcription Via the RNA pol II CTD which acts as landing pad
how is m7G cap added to the mRNA (capping)
- modified G is added to tri phosphate at 5’ end forming 5’ to 5’ bond
- methylation pf the CAP
what is the function of the CAP
- Protects mRNA from degradation by 5’-3’ nucleases
- Facilitates splicing
- Facilitates export from the nucleus
- Critical for translation of most mRNAs
- Functions mediated through protein binding
is the cap a protein binding element
yes
what are features of introns?
- Intron and exon boundaries contain conserved sequences
- 5’ splice site
- 3’ splice site
- Branch site
- Sequences define limits of exon and intron
- Sequences recruit the splicing machinery required to remove the intron and join the exons
what are purines and pyrimidines
Pyrimidine = C or U
Purine = A or G
what type of chemical reaction takes space in splicing
2 trans-esterification
what are the steps of 2 trans-esterification reactions
Step 1:
cut at 5’ splice site creation of bond between 5’ end of intron and branch site
Step 2:
cut at 3’ splice site to release intron lariat ligation of two exons
what is the spliceosome
Enzymatic complex that catalyses the removal of introns
what are the features of the spliceosome
- Requires ATP
- Large complex containing >200 proteins that assembles onto each intron
- Proteins include:
-RNA-binding proteins
-ATPases
-GTPases - Contains several snRNPs
-U1, U2, U4, U5 and U6
what are snRNPs (Small nuclear ribonucleoprotein particles)
- Stable RNA – protein complexes in the nucleus
- non coding RNA
- RNAs base-pair with conserved sequences in the intron (U1 with the 5’ splice site, U2 with the branch point)
- Splicing is catalysed by the snRNAs
what is the Sm ring
its a structure found in all snRNPs
what is the Sm binding site consensus
A/GAUUUUUGA/G
what percentage of patients with SLE have anti Sm antibodies
20
What sort of disease is SLE?
Auto-immune
True or false: transcription and splicing are functionally coupled such that they influence one another
True
what are the types of alternative splicing
- exon skipping
- intron retention
- Mutually exclusive exon
- Alternative 5’ splice site
- Alternative 3’ splice site
check slide 23 of the lecture
how are cis-acting sequences in pre-mRNA regulated
- Activators -binds to intronic (ISE) and exonic splicing enhancers (ESE)
- Repressors -binds to intronic (ISS) and exonic splicing silencers (ESS).
where does hnRNP bind
ESS
where does SR bind
ESE
