4 - Gene organisation and transcription II

Question 1

Where does the promoter lie on the gene?

Answer 1

At the start (5’ end).

Question 2

What is the anatomy of a gene?

Answer 2

It is made of introns and exons.

Question 3

What are exons?

Answer 3

Segments of the gene which contain sequences that form part of the final RNA

Question 4

What are introns?

Answer 4

Sequences in the gene which are transcribed but are edited out of the final mRNA.

Question 5

What is mRNA splicing?

Answer 5

Removing the introns in a strand of mRNA.

Question 6

What is the splice donor site?

Answer 6

AG|GU

Question 7

What is the splice acceptor site?

Answer 7

Pyr15NCAG.
Pyr = Pyrimidine base (C or U)
N = Any base

Question 8

What do introns start and end with?

Answer 8

Start with GU and end with AG.

Question 9

Sequence of events in mRNA splicing.

Answer 9

1. The small ribonucleic protein (snRNP) U1 binds to splice donor sequence.
2. U2, U4, U5 and U6. U5 binds to slice acceptor site.
3. This is the slicing complex - the spliceosome.
4. Cleavage of splice donor sequence.
5. The intron is removed as a lariat structure.

Question 10

How is the branch of the lariat structure formed?

Answer 10

The 5’ phosphate on the G forms a phosphodiester bond with the 2’ OH of the branch point A.