Transcription - Lecture 3

Question 1

True or False: The coding sequence in Prokaryotes and Eukaryotes in interrupted.

Answer 1

False, only the coding sequence in eukaryotes is interrupted

Question 2

What are the 3 main processing steps that take place in eukaryotic pre-mRNA?

Answer 2

• addition of 7MG cap
• addition of poly(A)tail
• removal of introns

Question 3

What are the splicing signals on eukaryotes?

Answer 3

5’ GU and 3’ AG sequence and A branch point

Question 4

Describe how a spliceosome removes introns.

Answer 4

• snRNP U1 binds to the 5’ splice site, snRNP U2 binds to the branch site
• The complete spliceosome assembles and cleaves the transcript at the 5’ splice site
• The 5’ end of the intron is joined to the A branch site to form lariat structure and U1 and U4 are released
• The 3’ splice site is cleaved and the 5’ of exon 2 is joined to the 3’ of exon 1
• The lariat shaped intron is released

Question 5

What is alternate intron splicing?

Answer 5

2 introns are removed to yield one mRNA or two introns and 1 exon are removed to yield a different mRNA

Question 6

What is multiple 3’ cleavage site splicing?

Answer 6

removal of introns by splicing at different spots on the pre-mRNA which results in mRNA of different lengths