NAGE 4 - mRNA Processing Flashcards
How does transcription in E. coli occur?
A sigma factor binds to TATAAA region. There is only one type of RNA polymerase. TFIID is used.
What is meant by RNA processing?
Initial RNA produced is the primary transcript, heterozygous nuclear RNA (hnRNA) or pre-mRNA. This RNA is then processed in the nucleus to mRNA.
What is the anatomy of a gene?
- The gene promotor is at the 5’ end of the gene.
- Segments of the gene that contain sequences that form part of the final RNA are called exons.
- The sequences edited out are called introns.
Describe the sequence of events in mRNA splicing.
1) U1 binds to the splice donor site. U2, U4 and U6 bind to the intron, and U5 binds to the splice acceptor site.
2) The assembly of the spliceosome triggers the hydrokysis of the AG - GU bond
3) The glycosine forms a temporary 5’ to 2’ bond with an adenosine residue on the intron, used as a branchpoint.
4) This triggers the hydrolysis of the splice acceptor site, and a lariat structure is formed.
5) The exons are then ligated together.
What type of molecule is U1, U2, U4, U5 and U6?
Small ribonuclear proteins or snRNPs.
What is the sequence at the splice donor site?
AG at the end of the exon and GU at the start of the intron.
What is the sequence at the splice acceptor site?
There are 15 pyramidines, then any base, then th CAG sequence.
What are the stages of post transciptional modification of mRNA.
A cap is added along side a poly adenyl tail. It is added one base at a time, 11-30 bases downstream from the AAUAAA sequence.
Why is the 7-MeG cap added to mRNA?
A 7-MeG cap is added to the 5’ end of the mRNA so that it is recognised by ribosomes. It also protects the mRNA from attack.
What disease is caused by a virus arracking the CAP?
Polio
Why is the poly-A tail?
It protects the mRNA strand, and gets shorter every time the mRNA is translated.
What causes thalassemia?
Thalassemia is caused by an imbalance in the amounts of the globulin chains. B-Thalassemia is a deficiency of B-chains. It is caused by splice site mutations.
What causes duchenne muscular dystrophy?
The gystophin gene is mutated - most DMD mutatioms are deletioms of one or more exons. These mutations cause dystrophin protein synthesis to be prematurely aborted.
