18.01.08 Splicing Flashcards Preview

DNA and chromosome structure > 18.01.08 Splicing > Flashcards

Flashcards in 18.01.08 Splicing Deck (5)
1

When and where does splicing occur?

In the nucleus pre-mRNA is processed to form mature RNA following 5' capping, 3' polyadenylation and splicing.

2

Summarise splicing.

Removal of introns by endonucletolytic cleavage and ligation of exons.

3

How is splicing mediated?

By the major and minor spliceosomes; complexed of snRNA molecules and >100 proteins.

Major snRNAs: U1 U2 U4 U5 and U6
Minor snRNAs: U11 U12, U4atac, U5 and U6atatc

4

What is the GT-AG rule

Introns begin with GT (GU) and end with a AG.

5

What are the sequential steps of pre-mRNA interactions with the snRNA complex?

1. U1 snRNA binds to donor splice site (“GU”) (via it’s complementary sequence: UACUUAC)

2. U2 snRNA binds to branch site (“A” nucleotide), U1 and U2 come together forming a loop in the pre-mRNA

3. U4, U5 & U6 associate with U1-U2 to form the spliceosome; U5 binds both donor & acceptor splice sites

4. Nucleophilic attack of GU (donor) by 2’ hydroxyl group of A of branch point, transesterification #1 (covalent link) forms lariat

5. Cleavage of acceptor (“AG”) transesterification #2 joins exons together

6. Lariat intron & spliceosome unbound