lecture 7 Flashcards
What does pre-mrna need to go through to be functional mrna?
it needs to be processed via splicing of introns
When will RNA not be transcribed?
when its in a functional state
What is the cap and polyA tail?
specific to eukaryotic mRNA
added post-transcriptionally to protect RNA from degradation to give stability and protection
Why does RNA polyermase II have a long conserved tail?
to recruit factors involved in stability and protection
What is the structure of the 5’ m7G cap?
All RNA polymerase II RNAs
RNA initially contains triphosphate at 5’ end between two bases
Second nucleotide in different orientation (added 5’ to 5’)
Methyl group added to top of base to change chemical behaviour
Capping two structure event: GpppN structure, methylation
What are the functions of the m7G cap?
Protects mRNA from degradation by 5’-3’ nucleases
Facilitates splicing
Facilitates export from the nucleus
Critical for translation of most mRNAa
Functions mediated through protein binding - CBP80/CBP20 in nucleus (processing/export), elF4 complex in cytoplasm (translation) - caps can bind to proteins for export of RNA to cytoplasm where it binds to eIF4 complex
What are the two key functions of capping?
mRNA protection and mRNA export
True or False?
m7G cap is encoded in the genome
False - added post-transcriptionally
What is the process of adding a polyA tail called?
polyadenylation
In mammals are introns or exons usually longer?
introns - generally between 80-10,000 nucleotides long
What are the conserved sequences in introns?
5’ splice site
3’ splice site
branch site
Why do intron and exon boundaries contain conserved sequences?
sequences define limits of exon and intron
sequences recruit the splicing machinery required to remove the intron and join the exons
What is the two step splicing process of introns?
1) cut at 5’ splice site, creation of bond between 5’ end of intron and branch site
2) cut at 3’ splice site to release intron lariat, ligation of two exons
What is a spliceosome?
enzymatic complex that catalyses intron-exon splicing in eukaryotes requiring ATP
Proteins include: RNA-binding proteins, ATPases, GTPases
-five small nuclear ribonucleoproteins (snRNPs)
What are small nuclear ribonucleoprotein particles (snRNPs)?
Stable RNA - protein complex 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)
What is splicing catalysed by?
snRNAs
What is anti-Sm?
anti-sm antibodies react against sm proteins
very rare antibodies unless you have the autoimmune disease lupus erythematosus
Why are transcription and splicing functionally coupled?
so that they influence one another
How many conserved sequences are involved in splicing?
three
what are snRNPs?
Rna protein complexes
True or False?
Splicing is an RNA catalysed event
true
How can splicing expand the proteome?
many genes have multiple introns
number of proteins»_space; genes in the genome
What are the different types of intron splicing?
Exon skipping
Intron retention
Mutually exclusive exons
Alternative 5’ splice site
Alternative 3’ splice site
How are alternative splicing mechanisms regulated?
Regulated cis-acting sequences in pre-mRNA
Activators - bind to intronic and exonic splicing enhancers (ISE and ESE)
Repressors - binds to intronic and exonic splicing silencers (ISS and ESS)
