exam 3 (regulatory RNA) Flashcards
What are typical functions of RNA
carrier of genetic information
Structural/catalytic component
Regulation of chromatin structure
Transcription
Where was RNA interference discovered
roundworm C. elegans
Why are C. elegans used as a model organism
- 50-60% of its genes have counterparts in humans
- worm is transparent
- 3 days to grow
- produce hundreds of descendants
- easy manipulation
RNAi silences gene expression in what manner?
sequence-specific manner
what 3 hypotheses were formed from C. elegans expressing green fluorescent protein, when they were fed bacterial dsDNA
- dsRNA alters target DNA
- dsRNA inhibits transcription
- dsRNA destabilizes mRNA
19% of C. elegans fall within ?
operons, which is highly unusual because they are rare in eukaryotes
how does RNAi silence gene expression
post-transcriptional repression:
dsRNA causes substantial reduction in mRNA levels of target gene, making it unstable
explain the RNAi silencing process
- double stranded DNA gets processed by a dicer into small interfering RNAs
- siRNAs are placed into RNA induced silencing complexes (RISC)
- siRNA guides RISC to target mRNA and cleaves it
function of RNAi
defense mechanism against viral infection, found in most eukaryotes
how is RNAi used in lab
tool for studying gene expression, genetics, genomics, and identification of gene phenotype
how can dsRNA influence C. elegans
C. elegans eat bacteria, and bacteria can express dsRNA, which can feeding of dsRNA can break down genes of C elegans
different organisms respond differently to dsRNA, in what form does dsRNA must be in to influence C. elegans and Drosophilia
LONG dsRNA
what happens if long dsRNA is injected into humans?
doesn’tt trigger RNAi, bu activates interferon response, nonspecific immune response that protects cells from pathogens
what are miRNAs
short ~22 nt RNA molecules that bind to mRNAs to block their translation or induce their degradation
how does miRNA contribute to mRNA destablization
shortens the mRNA poly(A) tails
result of miR-96 mutation ?
hereditary progressive hearing loss
result of miR-184 mutation ?
hereditary eye disease
result of miR-17~92 cluster deletion ?
skeletal and growth defects
what is the role of RNAi in fission yeast
influences chromatin structure
RNAPII transcribes repeated DNA where?
centromeres
how is RNA transcript repeated
RDRP transcribes a strand of RNA
what occurs after complementary strand of RNA is formed
they hybridize and are diced to form siRNAs, which mediate H3K9me3, compacting chromatin
what is piRNA
another class of small noncoding RNA (slightly bigger than miRNA), the last base is 2’O-methylated, increases piRNA stability
function of piRNA
involved in germline
- are antisense to transposons
- interact with piwi proteins to silence transposons
why do transposons need to be silenced?
could lead to mutations of important genes that would be passed on to the next generation
what are long noncoding RNAs (IncRNAs)
associate with chromatin modifiers and transcription factors to influence gene expression, performed by scaffolding protein-protein interactions
what allowed for the discovery of IncRNA
chromatin signature
H3K4me3 + H3K36me3 without associated protein-coding gene
explain the XIST IncRNA
transcribed from XIC and recruits protein machinery to establish heterochromatin
when IncRNA gets out of the nucleus and enters the cytoplasm, what is its function
they influence mRNA stability and translation, can act as miRNA sponges
