Post transcriptional control of expression & RNA interference

Question 1

What is alternative splicing?

Answer 1

single pre mRNAs can produce multiple products

Question 2

Give 2 examples of alternative splicing

Answer 2

1) Alpha tropomyosin gene , striated, smooth muscle synthesised as well as fibroplast and brain mRNA
2) Drosophilia melanogaster , different functions in nervous and immune system

Question 3

What is mutually exclusive splicing?

Answer 3

one of the exons in a cluster is included in functional transcripts

Question 4

How is alternative splicing regulated?

Answer 4

• in negative control, the presence of a repressor inhibits splicing
• in positive control, the presence of an activator allows splicing to occur

Question 5

What is the effect of mRNA editing on the final translated protein?

Answer 5

it increases the number of distinct proteins that can be encoded in a genome

Question 6

What is the role of UTRs in post transcriptional control?

Answer 6

• controls mRNA lifetimes
  controls mRNA stability
  -mRNA stability determines how much protein is translated in the cell

Question 7

Describe the mechanism of iron dependent regulation of Ferretin mRNA

Answer 7

-In low iron levels, IRP (iron regulatory proteins) bind to IRE (iron responsive elements)
- IRP blocks the ribosome from attaching to mRNA, so translation does not occur and ferretin production is reduced
- In high iron levels, iron binds to IRPs, preventing them from binding to IRE’s
- As a result IRP is prevented from blocking the ribosome and ferretin is produced

Question 8

How was RNA interference discovered?

Answer 8

Through injecting double stranded RNA which silenced gene expression

Question 9

How are siRNAs produced?

Answer 9

from double-stranded, foreign RNAs during RNA interference

Question 10

What are siRNAs?

Answer 10

• small double stranded RNAs 20-25 bp in length
• they silence specific genes through degradation of mRNA with complementary sequence

Question 11

Outline the mechanism of RNA interference

Answer 11

• foreign double stranded RNA is cleaved by DICER
• this produces double stranded siRNAs
• RISC (RNA-induced silencing complex is then formed ) to produce single-stranded siRNA
• foreign complementary single stranded RNA is then degraded by siRNA and RISC is released

Question 12

Give some uses of RNAi

Answer 12

experimental tool for specific gene ‘knockdown’ :
- cleavage of target RNA
-translational repression & eventual destruction of target RNA
- formation of heterochromatin on DNA from which target RNA is being transcribed
- also an experimental tool for genome- wide genetic screens
- and a tool to control infectious disease

Question 13

Give an example of RNAi in medicine

Answer 13

• used to treat transthyretin - mediated amyloidosis