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Genes: Organisation and Function > Lecture 17 > Flashcards

Lecture 17 Flashcards

1
Q

Coding RNA:

A
  • RNAs that encode some type of information
  • A conduite between the RNA and the protein
  • messenger RNAs
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2
Q

Functional RNA:

A
  • Ribosomal RNA
  • transfer RNAs
  • Decoding the information within the mRNA
  • short nuclear RNAs
  • part of processing RNA, splicing introns out of transcripts in eukaryotes
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3
Q

Regulatory (small) RNAs:

A
  • siRNAs (discovered through silencing RNAs)
  • miRNAs (discovered developmental mutants)
  • piRNAs
  • circRNAs
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4
Q

Regulatory (long) RNAs:

A
  • IncRNAs

- Involved with X inactivation in placental mammals

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5
Q

Gene silencing:

A
  • Trans-acting antisense RNA in E.coli silence their targets by forming dsRNA duplexes
  • 100 nt in size, complimentary sequences to mRNA
  • Selectively inactivate a gene/nucleotide sequence within a genome
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6
Q

Antisense inibition:

A

Paring between antisense and sense RNA, inhibiting gene expression as the duplex cannot be translated

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7
Q

Kemphues group and gene silencing experiment:

A
  • Anti-sense inhibition for silencing Par-1
  • Antisense mechanism cannot account for sense inhibition
  • Phenotype observed in half of the worms injected
  • Injection is easy, but the silencing effect is not easy to replicate
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8
Q

What does partition-1 (par-1) gene do?

A
  • It promotes early cell division in the nematode Caenorhabditis embryo
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9
Q

Can antisense/sense suppression be induced by aberrant RNA?

A
  • Gene silencing is mediated/induced by dsRNA

- 100x more effective than ssRNA

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10
Q

What does the unc22 gene code for?

A
  • Uncordinated-22
  • Codes for a muscle microfilament
  • Mutations in this gene result in twitching worms
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11
Q

Is gene silencing sequence specific?

A

Yes

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12
Q

What gene is unc24?

A
  • Paralysis
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13
Q

Fem-1 gene mutant:

A
  • No sperm, so feminises the worm
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14
Q

hlh-1 gene mutant:

A
  • Lumpy-dumpy phenotype
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15
Q

dsRNA causes

A
  • Loss of target mRNA, either because
  • dsRNA is interfering with transcription
  • dsRNA is causing degradation of the transcript, post-transcriptionally
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16
Q

Does gene silencing occur post-transcriptionally?

A
  • Yes!

- Injecting dsRNAs homologous to promoters and introns does not cause silencing

17
Q

RNA interference:

A
  • RNAi

- Eukaryotic cells perceive dsRNA as a sequence specific signal to inhibit expression of the corresponding mRNA

18
Q

Co-suppresion/post-transcriptional gnee silencing (PTGS)

A
  • Manipulate petal colour by introducing a transgene into plants
    WT flowers and transgenic flowers are produce
  • mRNA of transgene/endogenous gene are degraded
19
Q

Virus-induced gene silencing (VIGS)

A

Induce virus resistance by introducing viral transgene into plants

  • Expression of untranslatable viral transgene in plants, these plants are immune to virus as viral RNA/transgene mRNA is degraded
  • Non-transgenic plants exhibit disease symptoms as viral RNA accumulates
20
Q

Virus induced gene silencing:

A
  • Natural defence against viruses exists in some plants
  • Virus produce dsRNA either via secondary structures in the RNA or as a duplication event
  • dsRNA is recognised as being foreign, triggering RNAi
21
Q

RNAi is associated with small RNAs:

A
  • Antisense RNAs
  • Short interfering RNAs (siRNAs)
  • Target the genes/genetic elements from which they are derived
  • Work in trans and complementary to target
  • Induces mRNA degrading, post-transcription and sequence specific
22
Q

Discovery of endogenous small RNAs occured via:

A
  • Study of the lin mutant with altered patterns of cell lineage in vulva development
23
Q

Lin-4 mutant:

A
  • Bag of worms phenotype

- Vulva doesn’t form correctly, so eggs cannot come out of the worm

24
Q

Heterochronic mutants affect developmental timing (slowing it down or speeding it up):

A
  • Four stages of larval development
  • In lin-4 and lin-14(gf) there is a delay in developmental progression
  • Lin-14 and lin-28 loss of function shows developmental process earlier than normal
25
Q

Lin-14 mutation:

A
  • Required for the cell type of the first larval stage
  • The protein is only required for the first larval stage
  • But lin-14 mutants do not produce any lin-14 transcript so larval stage 1 is skipped
26
Q

Lin-4 mutation:

A
  • Stuck with L1 cell types in all four larval stages
  • Limits lin-14 activity to the l1 larval stage
  • Effects protein abundance
27
Q

Lin-14(gf) mutants with a loss of the 3’ UTR region show

A
  • 7 partially complementary sequences

- that the 3’ UTR region is essential for the degradation of the lin-4 protein in the 2nd, 3rd and 4th larval stages

28
Q

let-7

A
  • regualtes lin-41
  • found in all metozoans
  • works in larval development, regulating lin-41
29
Q

Primary miRNA is generated by:

A
  • RNA pol II and has a 5’ CAP and poly-A tail
30
Q

Primary miRNAs can form:

A
  • an imperfect hairpin stem-loop strucutre throuh the intramolecular interactions
31
Q

Drosher, a type III endonuclease:

A
  • Found in the nucleus
  • Recognises the hairpin loop, and binds to primary micro RNA transcript
  • precursor miRNA is exported from the nucleus
  • Produces a single duplex
32
Q

Dicer, another type III endonuclease:

A
  • In the cytoplasm
  • Type III endonuclease
  • Dices the precursor RNA, removes the loop from the stem
  • Produces multiple duplexes
  • 5’ phosphate and a 2nt 3’ overhang
  • Needs to be processed still further
33
Q

siRNA biogenesis

A
  • long perfectly pair dsRNA
  • it is processed in the cytoplasm by dicer
  • produces multiple duplexes
  • 5’ phosphate and a 2nt 3’ overhang
34
Q

RNA-induced silencing complex (RISC)

A
  • A complex that modifies dsRNA further
  • Argonaut degrades the target transcript leading to gene silencing
  • The end that enters RISC is determined by the sampling of thermodynamic stability of the 5’ end
  • The weakest end of the duplex enters

Genes: Organisation and Function (33 decks)

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