Gene Organisation and Transcription II Flashcards
What are the three terms for the RNA directly produced from transcription?
Primary transcript or Pre-mRNA or heterogenous nuclear RNA (hn RNA)
Where does RNA processing take place?
In the nucleus
What is the splice donor site?
Junction between exon and intron
What is the splice acceptor site?
Junction between intron and exon
What do exons end with?
AF
What do introns start and end with?
GU and AG
What are snRNP and what process involves them?
Small ribonuclear proteins and RNA splicing
Describe the process of splicing
snRNP U1 binds to splice donor sequence. 2. snRNP U2, U4, U5 and U6 bind then, forming the spliceosome. This formation cleaves the splice donor sequence. 3. The end G of the intron bends round and an ‘A residue’ in the intron acts as a branchpoint/2’ -OH and bonds in an intermediate step in splicing. 4. 2’ OH bonds/branchpoint forms between G and A residue. The phosphodiester bond beween end G of intron and the exon breaks so intron is removed as LARIAT structure. Adjacent exons are ligated together.
What two additional modifications do mRNA undergo, not including splicing?
PolyA tail addition and cap addition.
How is the mRNA cap formed?
By hydrolysis of terminal triphosphate of mRNA to a diphosphate. This then reacts with alpha phosphate of GTP to form 5’-5’phosphate linkage. Cap is further modified by Methylation at the N7 position in the purine ring to form 7-Methylguanylate cap.
What is the purpose of the mRNA cap?
To protect mRNA at the 5’ end and also greatly enhance translation
Where is the polyA tail added?
11-30 bases downstream of AAUAAA (polyadenylation site)
What is the purpose of the poly A tail?
Add stability
What can cause beta-thalassemia?
Splice site mutations in the beta globe gene
