Post-transcription Level

Question 1

What are the three major modifications?

Answer 1

1. 5’ capping
2. Polyadenylation
3. RNA splicing

Question 2

Describe the function of addition of 5’ cap

Answer 2

1. Protects growing primary mRNA chain from degradation by ribonucleases
2. Facilitates export of mature mRNA from nucleus to cytoplasm
3. Recognition of mature mRNA by ribosomes to initiate translation

Question 3

Definition of polyadenylation

Answer 3

addition of a long seq of adenine nucleotides at the 3’end of primary mRNA transcript to form poly(A) tail

Question 4

Describe the process of polyadenylation

Answer 4

1. Cleavage proteins recognise a (poly-A)
2. Pre-mRNA bends; stabilising factors stabilise new bent configuration
3. Endonucleases recognise poly(A) signal; cuts downstream in 3’UTR
4. Poly(A) polymerase synthesis the poly(A) tail by adding about 100-200 adenine nucleotide

Question 5

Definition of RNA splicing

Answer 5

Process that splices exon sequences of RNA and removes intervening intron sequences

Question 6

Before RNA splicing

Answer 6

• snRNAs associate with proteins to form snRNPs

- each snRNP contains a single snRNA molecule and multiple proteins

Question 7

Describe the process of RNA splicing

Answer 7

1. snRNPs and other proteins form spliceosome
2. snRNP base-pairs with nucleotides at splice site along introns
3. Spliceosome cleaves mRNA at 5’ splice site and intron is joined to a branch point within intron
4. Spliceosome the cleaves the mRNA at 3’ splice site/ exons are ligature together
   => excising introns