CMB2001/L07 Post-transcriptional Control I Flashcards
What is the difference in where translation occurs between prokaryotes and eukaryotes?
In eukaryotes, translation occurs outside of the nucleus
Give the 4 levels of eukaryotic gene expression regulation.
Transcription control
RNA processing control
Translation control
Protein activity control
When are the m7G cap and poly A tail added and what does this mean?
Added post-transcriptionally in eukaryotic mRNAs
Not encoded in the genome
What is pre-mRNA?
Unfinished messenger RNA or precursor mRNA
How is primary transcript processing coupled to transcription?
Via the RNA pol II CTD which acts as a landing pad
Describe the synthesis of the 5’ m7G cap. (2)
GpppN structure - addition of a guanosine triphosphate
Methylation - of guanosine cap which alters chemical behaviour of base and is crucial in function of mRNA
Describe the structure of the 5’ m7G cap. (2)
Methylated guanosine at N7 position
Linked to 5’ end via 5’-5’ triphosphate bridge
Give 3 functions of the m7G cap.
Protects mRNA from degradation by 5’-3’ nucleases
Facilitates splicing
Facilitates export from nucleus
Critical for translation of most mRNAs
Functions mediated through protein binding
What kind of element is the 5’ cap?
Protein-binding
How long are introns generally?
80-10,000
What is a Duchenne muscular dystrophy?
Muscle wasting disease
Linked to gene dystrophin
What 3 conserved sequences are present in introns?
5’ splice site
Branch site
3’ splice site
Give the 2 steps of intron splicing.
2 trans-esterification reactions
1) cut at 5’ 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 kind of proteins are within the spliceosome? (3)
RNA-binding proteins
ATPases
GTPases
Several snRNPS (U1-2, U4-6)
What is splicing catalysed by?
snRNAs
What do snRNPs bind to?
Base-pair with conserved sequences in intron
(U1 with 5’ splice site, U2 with branch point)
What do snRNAs code for?
Nothing - non-coding
Where are snRNPs found?
In the nucleus
What are anti-Sm antibodies and which disease is associated with them?
Reactant against Sm proteins
Systemic lupus erythematosus (SLE)
What are SM proteins?
Essential components of snRNPs which aid in assembly and stability
How are transcription and splicing functionally coupled?
Such that they influence one another
Why is the number of proteins more than the number of genes in the genome?
Alternative splicing allows many proteins to be made from the same genes
Give 3 types of alternative splicing.
Exon skipping
Intron retention
Mutually exclusive exons
Alternative 5’ splice site
Alternative 3’ splice site
Where do activators bind?
Intronic (ISE) and exonic splicing enhancers (ESE)
Where do repressors bind?
Intronic (ISS) and exonic splicing silencers (ESS)
How can mutants cause defects in splicing?
Loss of protein function
Only one protein isoform
What is the effect of spinal muscular atrophy on infants?
Most common genetic cause of infant mortality
What are the effects of retinitis pigmentosa?
Reduced visual capabilities and blindness
What is the spliceosome?
Enzymatic complex that catalyses the removal of introns
