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Control Of Gene Expression > Rna degradation/turnover > Flashcards

Rna degradation/turnover Flashcards

1
Q

Why is rna degraded sometimes

A

Damaged mrna Eg incorrect editing

Or to control gene expression levels

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2
Q

What can mrna half life be increased by (reduced turnover/degradation)

A

Stability Eg via poly A tail, 3’ utr

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3
Q

For degradation. What needs to happen to mrna

A

De circularisation by removing either cap or poly a tail

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4
Q

What 3 enzymes are involved in phase 1 degradation

A

Decapping enzymes (eg dcp 1 or 2)

Endonucleases

Deadenylases

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5
Q

Give an example of an endonuclease in phase 1 degradation

A

Argonaute

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6
Q

What is the most famous deadenylase

A

Ccr/not

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7
Q

Do both cap and poly a need removed for degradation

A

No. One or the other is fine for exonucleases activity

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8
Q

How do endonucleases like argonaute work

A

They cleave rna in the middle which means either cap or poly a is attached. Allows degradation

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9
Q

Which exonucleases 5’ to 3’ functions after decapping

A

XRN1

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10
Q

What is XRN1 for

A

Rna turnover and processing

Also involved in txn termination early (5’ end)

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11
Q

What is the diff between turnover and processing

A

Processing is just degradation of a part of rna

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12
Q

Which complex has 3’ to 5’ exonuclease working after deadenylation

A

Exo some complex

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13
Q

What are the 2 3’ to 5’ exonulceases in the exosome complex

A

Rrp6 and 44

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14
Q

What is deadenylation dependant decay

A

Overtime there is gradual loss of poly A via deadenylases like ccr not

This can cause degradation via exosome activity rrp6 and 44

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15
Q

What 4 things trigger deadenylation dependant decay via ccr not

A

AU rich sequences (AREs)
Nonsense codons (PTCs)
C fos coding sequences
Mirna

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16
Q

Deadenylation independent decay is endonuclease activity (argonaute) or what else

A

Auto regulation of own mrna translation levels

17
Q

Give an example of auto deadenylation regulation independent decay

A

RPS 28B ribosome protein recruits edc3 decapping protein to recap it’s own mrna for degration

18
Q

What is degradation due to nonsense codons called

A

Nonsense mediated decay nmd

19
Q

What are premature stop codons PTCs due to

A

Errors in txn, splicing, editing, polyadenylation or mutations

20
Q

Stop codons are usually in final exons. What constitutes a target for nmd

A

A ptc which is above 55 nucleotides from the last exon junction

21
Q

What bind close to exon junctions which get cleaved by ribosomes

A

Exon junction complexes EJCs

22
Q

If a ptc occurs 55 above nucleotides before a last exon junction what happens

A

Ejc will stay there as ribosome will stop prematurely so can’t cleave it

This ejc will attract UPF proteins which causes rna degradation

23
Q

What is process of nmd called

A

Surveillance

24
Q

Out of siRna and mirna. Which one makes a perfect complimentary binding to mrna

A

SiRna

25
Q

are si rna and mi rna diff in size

A

No. Both 21-23 nucleotides long

26
Q

Which out of si rna and mi rna is a viral defence mechanism (get it from ds viral rna)

A

Si rna

27
Q

How does si rna degrade rna from virus

A

The ds rna from virus is cleaved and unwound by dicer

1 strand binds with the risc complex which has endonucleases like argonaute

Cleaves in the middle of mrna allowing degradation (independent decay)

28
Q

What is mi rna for

A

Blocking translation and further degradation

29
Q

How is mirna made

A

Mirna gene is processed by drosha enzyme
Then exported out by exportin 5

Cleaved and unwound by dicer

Binds with risc complex

Binds to the 3’ utr stopping translation and causing degradation

30
Q

Are longer utrs or short utrs required for mirna blocking translation

A

Longer utrs (usually in slowly growing cells)

31
Q

Why is it good fast growing proliferating cells have short utrs

A

Less mirna binding sites. They can’t block translation because they need proteins for growth

32
Q

What can si rnas be used for

A

Research into knock down genes

Control Of Gene Expression (13 decks)

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