16. miRNA & siRNA

Question 0

miRNA

Answer 0

evolutionarily conserved
small non-coding RNAs that regulate gene expression via inhibition & degradation of mRNA (Eukaryotes)
PARTIALLY complementary to target mRNAs

Question 1

RNAi

Answer 1

RNA molecules inhibit gene expression, usually through destruction of specific mRNA molecules

Question 2

siRNA

Answer 2

small interfering RNA – short, double stranded RNA molecules that selectively degrade mRNA

form chromatin structures that inhibit gene expression

PERFECT complementary to target mRNAs

Question 3

miRNA synthesis

Answer 3

1. RNA pol II makes primary miRNA (forms stem loop)
2. pri-mRNA —> pre-mRNA via DROSHA
3. pre-miRNA transported from nucleus to cytoplasm via exportin5-RanGTP
4. pre-miRNA processed into a small miRNA duplex via DICER, assembles into RISC, inhibits translation

Question 4

functional strand in P body

Answer 4

retained to provide specificity and guidance to the target mRNA

Question 5

passenger strand in P body

Answer 5

removed & degraded

Question 6

siRNA

Answer 6

not made in cells (introduced externally)

double stranded, form RISC

perfect complementary

Question 7

methods of siRNA introduction to cells?

Answer 7

aptamer-conjugated siRNA
cholesterol-conjugated siRNA
liposomal formulated siRNA
antibody complex

Question 8

miRNA: translation repression

Answer 8

miRNA guides the complex to target mRNA sequence, binds w/partial homology to mRNA, prevents translation

Question 9

mRNAs bound by miRNA are stored where?

Answer 9

P-bodies

contain argonaute & Dcpla ***this is where translation suppression occurs

Question 10

siRNA uses?

Answer 10

exogenous dsRNA pathway

has perfect homology, leads to direct cleavage/degradation

(miRNA uses endogenous Rna)

Question 11

miRNA & siRNA can both use?

Answer 11

transcriptional repression
both associate with RITS
causes change in chromatin structure (helps heterochromatin stabilize–methylation) so that transcription is suppressed

Question 12

how can miRNAs act as oncogenes?

Answer 12

cause overexpression of growth cell genes, by inhibiting apoptosis & allowing proliferation of cancer cells & inhibiting genes that prevent apoptosis & inibiting genes that regulate cell proliferation

Question 13

similarities between transcriptional factors & miRNAs

Answer 13

plieotropy 
combinatorial & cooperative activity 
accessibility 
regulation 
network motifs