MCB 121 Lecture 13

MCB 121 Lecture 13 - MCB 144- Lecture 13 I. Architecture of...

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MCB 144- Lecture 13 I. Architecture of mRNA II. Mechanism of Intron removal A. Chemistry B. SnRNAS C. Splicesome D. Evolution-RNA world E. Non snRNP's - fidelity ------------------------------------------------------------------------------------------------------------------------- Central Dogma: DNA => RNA => protein (pre-mRNA => mRNA) * DNA is transcribed to make pre-mRNA * pre-mRNA is processed in several different way to make a mature mRNA * mature mRNA is used for protein synthesis What is pre-mRNA? - Sequence of DNA contains promoter region, transcriptional start site, introns (non-coding region) and exons (coding regions) - pre-mRNA is processed co-transcriptionally to make mRNA - what happens to pre-mRNA: 1) 7mG cap is added onto the 5' of the pre-mRNA (5'-5' linkage between the nucleotide) 2) poly A tail is added to pre-mRNA by poly A polymerase (without template) * Cap + poly-A tail = required for the initiation of translation * interact with each other to recruit part of ribosome at the 5' end of the mRNA 3) splicing => these three steps occur in nucleus
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5' UTR = untranslated region 3' UTR RNA would start initiate translation at the first AUG from the CAP (unlike prokaryote) => eukaryote ribosome recognizes the CAP and binds to it => at AUG is where the full ribosome meet and translation starts mRNA is then exported into cytoplasm (where translation occurs) # of introns per gene in species varies: Yeast => most genes have no intron => some has 1 intron, fewer has 2 introns Mammal => average of 7 introns/gene => exons are small (150 nt) compared to intron (>100kb) => lots of introns allow alternative splicing and create different proteins (isoform) * different coding regions would encode different protein products * make different protein isoform! (variation of the same protein) => allow for proteins diversity and complexity in different species Mechanism : - AG|GURAG is the splice donor sequence - it's the junction between exon 1 and the intron - intron sequence isn't well conserved (GURAG) * second one is the purine (can be A or G) * third one is the pyrimidine (can be U or C) - A = branch site - between "A" and "AG" = poly pyrimidine tract (U/C)
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To know where are the introns=> look cDNA structure cDNA are made after splicing of intron
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This note was uploaded on 05/09/2010 for the course MCB 121 taught by Professor Gasser during the Winter '09 term at UC Davis.

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MCB 121 Lecture 13 - MCB 144- Lecture 13 I. Architecture of...

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