Lecture 28 Flashcards
What does hnRNA need for become a mature RNA?
- 5’ cap
- 3’ poly tail
- to splicing unused mRNA
What is mRNA capping?
it is added before transcription occurs
- the RNA will remove one phosphate and the 7 methyl Guanine will be added to the end backwards
- nuclease don’t understand it so they can’t degrade it
Explain the transcription termination and polyA- tailing
(polyadenylation)
-The Cleavage signal sequence (AAUAAA) gets recognized by a endonuclease and it will cleave the RNA downstream from the sequence
- a useless fragment will be taken up by the cell
- a polyadenylate polymerase will add 80-250 Adenosines and a tail is formed
What is splicing?
when the intron (non coding regions) are taken out leaving the exons (coding regions) to be covalently linked together
How did they find out about introns
They noticed parts of the gene would loop. Those loops contained the introns and were called R-loops
How can mRNA be identified?
in affinity chromatography, the resin will be T’s since every mRNA has a polyAtail, you can identify all your mRNA’ s in the cell
explain how introns are taken out
they cleave at a 5’ splice site and form a loop “lariat” at the 3’ splice site. Then they cleave at the 3’ splice site out of the exon. The exons are connected together.
Why are introns made if they are going to be taken out?
they are important to the cell and allow regulation of mRNA
what indicates the splice site?
- on the 5’ splice site, its G-U
- the branch point (A)
- the 3’ slice site, A-G
what are the 2 transesterifications
1) branch point attacks the phosphate at the 5’ splice site
2) the 3’ hydroxyl of exon 1 attacks the phosphate of the 3’ splice site
now the lariat is free and the phosphate on exon 1 attaches to the exon 2
what are snRNP? what do they do?
they are small nuclear riboprtieins that move the exons in the correct orientations so the transesterifocation can occur
group 1 splicing
the intron didn’t have a branchpoint, the exogenous guanosine acts like the branchpoint. so not lariat is formed
group 2 splicing
the intron has a branch point
what is alternative splicing?
it allows for protein diversity
ALL introns are removed but some exons can be taken out as well alternate forms are called isoforms
