Lecture 8 Part 2 (lec 9)

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25 Mar 2012
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Lecture 9 Feb. 16/12
Transcription II (PII)
mRNA creation from RNA
1) 5’ pre-mRNA capping added to protects RNA from exonucleases
Phosphatase removes a phosphate from 5’ end
GMP is added by guano transferase
Methyl group is added by methyl transferase to complete capping
Pre-mRNA RNA splicing
Modification of RNA after transcription to create mRNA/prepare it for translation
Transcribed introns are removed (non-coding) and exons are joined together
(coding)
Catalyzed by spliceosome
1) Adenosine attacks 5’ splicing site on exon
2) 5’ of on exon reacts with 3’ of other to release intron
Termination of mRNA
1) CDSF and CtsF move from CTD on RNAPII to specific sites on transcribed mRNA
2) CDSF and CtsF help signal additional cleavage factors
3) RNA becomes cleaved
4) Protein PAP adds polyA (multiple adenosine monophosphates) tail to 3’ end of mRNA
5) Addition of polyA tail is called polyadenlyation, mRNA is fully transcribed
6) mRNA exported from nucleus to cytoplasm to be translated in ribosome
Translation
Steps in ensuring correct translational unit pairing
1) tRNA synthetase (aminoacyl tRNA synthetase)
Makes sure correct tRNA has correct AA
Editing site cleaves off incorrect AA through hydrolytic editing
2) tRNA molecule
Makes sure correct tRNA pairs with correct mRNA codon
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