Lecture 8

Question 1

what three steps are specific to eukaryotes?

Answer 1

• 5’ capping
• RNA splicing
• 3’ polyadenylation

Question 2

what occurs in RNA Pol II that is crucial for mRNA processing proteins and why?

Answer 2

CTD phosphrylation because processing factors for capping, polyadenylation, splicing etc are attached to Pol II CTD tail and hop to specific pre-mRNA ites during its transcription

Question 3

why do we have modifications of 5’ and 3’ end of mRNA

Answer 3

Distinguishes mRNA from other RNA molecules
Stabilises mRNA
Required for efficient translation
Allows mRNA to be properly processed and expressed to the cytosol

Question 4

how does capping of 5’ end of pre-mrna occur

Answer 4

phosphatase cleave off 1st phosphate at 3’ end
guanyl transferase adds a guanyl group to the phosphate end
methylated by methyl transferase at base
second methylation may also occur

Question 5

4 crucial proteins for polyadenylation

Answer 5

CPSF - cleavage and polyadenylation specificty factor
CstF - cleavage stimulation factor F
PAP - poly A polymerase
PABP - poly A binding protein

Question 6

what is the polyA tail used for?

Answer 6

anayltics - amplify mRNA because we can design polyA primers to bind to this.
stability - prevents digestion.

Question 7

splicing

Answer 7

2 step transesterification to remove the introns and ligate the exons because it is the exons that code for the protein

Question 8

what is the spliceosome made up of?

Answer 8

snRNPs

Question 9

what is the average size of an exon

Answer 9

150bps

Question 10

what do cells reply on for splicing?

Answer 10

snRNPs

recruitment of SR proteins and hnRNPs

Question 11

what do hnRNPs do?

Answer 11

hnRNPs package introns and mark them, bring the 2 ends of the 3’ and 5’ intron sites together

Question 12

what is splicing used for?

Answer 12

generation of templates for translation (converts pre-mRNA into accurate mRNA)
alternative splicing - diversity