Lecture 7 - Control Of Gene Expression 2

Question 1

What are the 4 types of alternative splicing?

Answer 1

1. Alternative 5’ splice site selection
2. Alternative 3’ splice site selection
3. Exon inclusion or skipping
4. Intron retention

Question 2

What is an example of alternative splicing?

Answer 2

alpha-tropomyosin RNA can be alternatively spliced into:
1. Striated muscle mRNA
2. Smooth muscle mRNA
3. Fibroblast mRNA
4. Brain mRNA

Question 3

What is an isoform?

Answer 3

A possible splicing pattern meaning different proteins can be made from the same mRNA

Question 4

How is alternative splicing regulated?

Answer 4

Negative control: a repressor is added to stop splicing
Positive control: an activator is added to initiate splicing

Question 5

What 3 things can RNA editing involve?

Answer 5

1. Addition or deletion of uridine to mRNA
2. Deamination of adenine producing inosine
3. Deamination of cytosine producing uracil

Question 6

What is an example of RNA editing?

Answer 6

Apo-lipoprotein B can have Deamination of cytosine to uracil:
If cytosine isn’t converted - the protein is made in the liver as lipoproteins
If cytosine is converted to uracil a stop codon is made and the protein is made in the intestine for fat absorption

Question 7

What is an ORF

Answer 7

An open reading frame that is a stretch of codons beginning with the start codon (AUG) and ending with a stop codon (UAA, UAG, UGA)

Question 8

How can UTRs control mRNA stability with an example?

Answer 8

Since iron is toxic if circulating at high levels, a transferrin receptor controls iron uptake into the cell.
At low iron levels the transferrin mRNA is stable and iron is transported but at high levels the mRNA degrades and no iron is transported

Question 9

How may UTRs control mRNA translation with an example?

Answer 9

Ferretin binds iron to prevent it from being toxic:
At low levels translation is blocked but at high levels translation occurs

Question 10

Why are C.elegans used as model organisms?

Answer 10

Cheap and easy to grow in Petri dishes, low generation time, can be stored frozen

Question 11

How did Fire and Mello discovered RNAi in 1998

Answer 11

• injected double stranded RNA to reduce expression of specific genes
• does so by reducing levels of mRNA
• RNAi is sequence specific

Question 12

What is the mechanism of RNAi?

Answer 12

Single stranded RNAi bind to foreign RNA and are degraded