CMB2001 Exam Questions With
Verified Answers
Why does RNA degradation take place? - answerDamaged mRNA
Incorrectly transcribed/processed mRNA
Control gene expression
What 2 things control mRNA levels? - answerTranscription and turnover
Why is turnover important? - answerIf mRNA has a ridiculo...
Why does RNA degradation take place? - answer✔✔Damaged mRNA
Incorrectly transcribed/processed mRNA
Control gene expression
What 2 things control mRNA levels? - answer✔✔Transcription and turnover
Why is turnover important? - answer✔✔If mRNA has a ridiculously long half life and doesn't go
away, then if you stop transcription you don't stop protein expression because the mRNA is still
there
Describe what casein mRNA is and explain the importance of turnover - answer✔✔Expressed in
mammary glands
mRNA increases ~70fold on stimulation by prolactin
But transcription only increases ~2 fold
HOW?
- Half-life increases dramatically (~40fold) in response to prolactin
- Poly(A) tail length is increased which is an indication of the mRNA being stabilised
- 3'UTR of RNA binds proteins which aid in this stabilisation
What do mRNAs look like during translation? - answer✔✔Circular
Why is the mRNA circular during translation? - answer✔✔Monitors mRNA integrity - it will not
be circular if it has lost the cap or poly(A) tail
Bring ribosomes ending translation close to the AUG (it is suggested that ribosomes recycle onto
the 5' end)
Helps translation because it helps reinitiation of translation
Stabilises the RNA because most processes that target RNA for degradation start through either
the cap or the poly(A) tail and to get to these you have to break open the circular structure
Describe Phase 1 of mRNA degradation - answer✔✔The breakdown of the RNA
Start by either removing the Poly(A) tail and/or the cap to make it accessible for exonucleases
Decapping enzymes - DCP1, DCP2
Endonucleases - Argonaute, Swt1, Smg6
Deadenylases (remove the poly(A) tail) - Ccr/Not complex
Describe Phase 2 of mRNA degradation - answer✔✔Degrade with exonucleases
5' to 3' exonuclease
3' to 5' exonuclease
What is the exosome? - answer✔✔The exosome is the main 3' to 5' exonuclease in the cell
It is involved in RNA turnover and processing
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