Lecture 31 & 32 Flashcards
which introns are autocatalytic
Group I and II
intron first hypothesis
Introns-first: In the “RNA world” introns could allow reshuffling functional RNA fragments by splicing them together
Intron early hypothesis
Introns-early: Introns in-frame allow for protein domains to be reshuffled in genes, prokaryotic introns lost over time once gene complexity established
Intron late hypothesis
Some introns continue to be lost or gained as species evolve and change
describe splicing fidelity
for genes with more than one intron, RNA may splice in different spots
What is one way to ensure splice sites aren’t skipped
initiating splicing during transcription
3 things
what can splicing control
Alter coding region, remove/include RNA regions which modify stability or how well it binds ribosomes affecting the rate of translation
Coding region, stability, translation rate
6 ways alternate splicing can generate protein variability
(A) Constitutive splicing
(B) Mutually exclusive exons
(C) Alternate exon / exon skipping
(D) Alternate 3′ splice site
(E) Alternate 5′ splice site
(F) Intron retention
What is the P element
transposable element that used to only be in fruit flies which was found to be in all wild flies today
WHat heppens if a P element is put into a human cell
always splices properly
What is the PSI? Where is it expressed?
P-element splice inhibitor
Binds the 5’ splice site at the end of exon 2 and blocks U1 binding
PSI is expressed in low levels in ovaries and testes so splicing is normal and transposase is made
What are the two P element proteins
66 kDa somatic protein that acts as a repressor blocking DNA from being cut and blocking the promoter
87 kDa germline protein is the transposase which binds the same sequence and cuts the DNA and inserts the element at a new location
They are self limiting
What happened when a wild female had p elements and they bred with a lab male? Inverse?
Wild female had p elements their whole life
so they had many repressor proteins that
was passed down to the offspring
when the father had the P element, there were no repressors in the egg and it was a defective baby
Is the P elements self-limiting? what happens when inserted into an uncolonized genome
Yes, they will rapidly insert until established enough to self-limit
Example of RNA interference
when a gene was added to petunias to make it more purple, it became white
RNA is interfering with the function of the normal RNA
What are miRNA
short non-coding RNA molecules that downregulate target genes at the post-transcriptional level
gene control
What are the two fates observed from miRNA binding a target mRNA
silencing
destruction of mRNA
Single miRNA targets multiple genes or vice versa?
both are possible
What is a primary-miRNA
dedicated transcript for the miRNA
What is RISC
RNA induced silencing complex
small RNA
Silencing vs degradation
a small RNA can be partially complementary or fully-paired with a target
Partial match: translation inhibited’
Full match: mRNA is cleaved and rapidly degraded
is the miRNA conserved
yes
why does mismatch miRNA matter
mismatched miRNA can accommodate many more targets and be used as an additional control mechanism to downregulate translation of multiple genes simultaneously
what is a tighter match
Higher chance of silencing
what is miR-1? What does deletion lead to
miRNA required for muscle heart muscle development
Deletion in mice leads to lethality and heart defects
what are up-miRNA?
miRNA that enhance translation
What is FXR1
RNA binding protein that recognizes which miRNA are up-miRNA
What do miRNA do in the heart
Promote development by affecting transcription factors HOXA11 and histone modification (HDAC4)
Affects heart growth, differentiation and cardiac rhythm
miRNAs in the blood are a marker of tissue damage after heart attack
5 steps
describe the biogenesis of miRNA
a gene containing a miRNA sequence is transcribed
the microprocessor complex recognizes stem loop and cleave it off leaving hairpin
dsRNA stem-loop is now a pre-miRNA and is exported out of the nucleus
Dicer cuts the miRNA down to 21 nt
RISC uses this miRNA to find and act on targets
