Lecture 12

Lecture 12 - LS3 MOLECULAR BIOLOGY LECTURE 11 Overview...

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LS3 MOLECULAR BIOLOGY LECTURE 11 Overview Eukaryotic Genes and mRNA Processing Dr. Randolph Wall Reading: Watson et al., 371-374, 379-387, 391-395, 398-403, 406-409
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mRNA Processing Events in Eukaryotes: 5’cap addition RNA Splicing 3’polyA addition pre-mRNA mRNA AAAAA 3’ eukaryotic gene 5’ UT 3’ UT AAUAAA
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Functions of 5’ Cap and 3’ PolyA •Resistance to degradation •Transport out of nucleus •Translation initiation •mRNA stability and turnover Molecular biologists use PolyA tail to purify mRNA away from rRNAs and tRNAs PolyA is used in cloning mRNA (cDNA cloning)
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The Splicing Reactions Cleavage at 5’ intron/exon Cleavage at 3’ intron/exon Junction & 5’ exon -> 3’ exon splicing
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Spliceosomes Carry Out mRNA Splicing •Splicing is carried out in a very large complex of RNA & protein called the spliceosome (similar in size to ribosome!) •Composition of spliceosome •5 snRNPs (small nuclear ribonucleoprotein particles (snRNPs, called “SNURPs”) •uridine-rich small nuclear RNAs; U1, U2, U4, U5, U6 snRNAs •~150 proteins •Roles of snRNAs in splicing •U1 binds 5’ splice site, U2 binds intron branch site A •U4-U5-U6 complex brings 5’ •U6 catalyzes 5’ splice site •U5 mediates 3’ splice site cleavage & 5’ exon joining to 3’ exon •snRNP functions carried out by spliceosome uridine-rich snRNAs, rather than proteins
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One Gene ---> One mRNA: Simple Splicing One gene ---> multiple mRNAs: Alternative Splicing Alternative splicing generates different mRNAs from the same pre-mRNA, This produces different proteins from a single eukaryotic gene
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LS3 MOLECULAR BIOLOGY LECTURE 12 May 8, 2008 TRANSLATION I: GENETIC CODE AND TRANSFER RNA (tRNA) Dr. Randolph Wall Reading: Watson et al., 411-423, 461-477
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Gene Expression Transcription: DNA -------> RNA same language (nucleotides), different font Translation RNA ------> protein new language (nucleotides -----> amino acids), translation required
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Translation Overview •Genetic Code (mRNA) –Open Reading frames (ORFs) -Degeneracy •tRNAs (translators) –Charging by tRNA synthetases –Wobble pairing (between tRNA anticodon & mRNA codon •Ribosomes (protein synthesis machines) –rRNA, ribosomal proteins, other proteins •Phases of Translation –Initiation: very different in prokaryotes & eukaryotes –Termination:
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Overview of the Processes in Translation: The ribosome cycle
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Lecture 12 - LS3 MOLECULAR BIOLOGY LECTURE 11 Overview...

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