RNA processing Flashcards
What are two forms of dsRNA in the normal eukaryotic cell?
miRNA and rRNA (ribozymes)
What is a major difference between promoters and terminators?
Promoters not trasnscribed
terminators are transcribed
Why are eukaryotic genes interrupted?
- Expands repertoire of gene products via alternative splicing
- Expand the target size of genes, increasing genetic diversity by enhancing the rate of crossing over by hmologous recombination
(genes are more spread out by introns)
- regulatory advantage (splicing is regulate)
When does mRNA processing occur?
co-transciptionally
What is special about the 5’ guanyl cap?
It protects the mRNA strand from being degraded
It has an abnormal 5’ to 5’ linkage
Added Co-transciptionally
Binding by proteins allows exit from nucleus
What is a primary transcipt (pre-mRNA)?
mRNA that still contains introns
Why do the ends of the mRNA strand need to be modified?
- transport out of nucleus into cytoplasm
- Increased stability
- translational effeciency
Where is mRNA splicing performed in the cell?
In the nucleus co-transcriptionally
Explain the function of small nuclear ribonucleoprotein particles (snRNPs)?
They assemble on the RNA at the intron sequence, cut out the intron, and rejoin the RNA chain, releases intron fragment in the form of a lariat (lasso)
RNA SPLICING MECHANISM:
catalyzed by snRNPs
adenine within intron attacks 5’ splice site and cuts the sugar-phosophate backbone of the RNA,
eventually the free 3’-OH end of first exon sequence reacts with the beginning of the next exon=rejoining
What is special about the lariat?
It could only be possible with RNA because RNA has a hydroxyl group on it’s 2’ and 3’ end. So a unique 5’ to 2’ phosphodiester linkage is formed!!
The lariat is eventually degraded
What is a U-snRNP?
set of proteins plus a uracil-rich RNA (U1 snRNA or U2snRNA)
