Bio 3000 - Capping and Polyadenylation.
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Are Caps coded for by DNA?
No, neither are "Tails".
What are the roles of the 5' Cap?
- Protection from Nucleases.
- Localization (Transport).
- Direction to Ribosomes (Translation).
Is RNA or DNA capped?
RNA is, DNA has telomeres.
What is the structure of the 5' Cap?
- 5' to 5' Triposphate linkage.
- Methylation of N7 site.
- Methylation of the 2' OH.
Where does the Methyl come from in Methylation of the 2' OH?
What is the purpose of 5' to 5' Triphosphorylation?
It prevents the Cap from being recognized by Nucleases, increasing stability.
What is the purpose of RNA Triphosphate in Capping?
Removing the γ-Phosphate to create a GDP residue.
What is the role of Guanylyl Transferase in Capping?
To add GMP to the Cap (GTP -> GMP -> Cap).
What is the role of Methyl Transferase in Capping?
Methylating the N7 & the 2' Ribose.
When does Capping Occur?
Very early on in Transcription.
To which end of the mRNA is CAP added?
To which end of the mRNA is the Poly-A Tail Added?
How is Guanine added to the Cap?
- The 5' GTP has it's γ-Phosphate Removed by Triphosphatase.
- Guanylyl Transferase Adds GMP from GTP to the 5' end.
- Methyltion Occurs.
How is the Poly-A Tail added?
- 1. The 3' end is Cleaved and Degraded.
- 2. The Poly-A Tail is then attached to the remaining 3' end.
What is a Polyadenylation Signal?
The Consensus Sequence found upstream of the Polyadenylation Site that indicates Polyadenylation should occur.
What is the Mammalian Polyadenylation Signal?
AAUAAA (Found ~2-nt upstream of Polyadenylation Cleavage Site).
There is a consensus sequence relating to Polyadenylation downstream of the Polyadenylation site. True or False?
True, it lies 23-24nt downstream of the cleavage site.
How is the cleavage site recognized?
Consensus sequences at the site and surrounding it.
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