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Transcript
Half Hollow Hills High School Ms. Foglia AP Biology Chapter 17. RNA Processing AP Biology 2004-2005 Transcription -- more details The process of transcription includes many points of control where to start reading DNA where to stop reading DNA editing the mRNA protecting mRNA as it travels through cell AP Biology 2004-2005 2004-2005 1 Half Hollow Hills High School Ms. Foglia AP Biology The Transcriptional unit 20-30b 5’ RNA TATA polymerase TAC transcriptional unit 3’ DNA ACT DNA introns promoter transcription start transcription stop 3’ pre-mRNA AP Biology 5’ 2004-2005 Transcription controls Promoter TATA box where RNA polymerase attaches to DNA Transcription start where RNA polymerase starts transcribing DNA Transcription stop where RNA polymerase stops transcribing DNA Pre-mRNA AP Biology 2004-2005 initial product of transcription 2004-2005 2 Half Hollow Hills High School Ms. Foglia AP Biology Transcription factors proteins which bind to DNA & turn on or off transcription “master regulators” genes controlling development AP Biology 2004-2005 Primary transcript Processing mRNA AP Biology 2004-2005 protecting RNA from RNase in cytoplasm add 5’ cap add polyA tail remove introns 2004-2005 3 Half Hollow Hills High School Ms. Foglia AP Biology Protecting RNA 5’ cap added modified G (GTP) protects mRNA from RNase (hydrolytic enzymes ) 3’ poly-A tail added 50-250 A’s protects mRNA from RNase (hydrolytic enzymes ) helps export of RNA from nucleus AP Biology 2004-2005 Dicing & splicing mRNA Pre-mRNA → mRNA edit out introns intervening sequences splice together exons expressed sequences In higher eukaryotes 90% or more of gene can be intron no one knows why…yet there’s a Nobel prize waiting… AP Biology 2004-2005 2004-2005 4 Half Hollow Hills High School Ms. Foglia AP Biology snRNPs Spliceosome recognize splice sites ribozymes catalyze process small nuclear ribonucleoproteins AP Biology 2004-2005 Splicing details No room for mistakes! editing & splicing have to be exactly accurate a single base added or lost throws off the reading frame AP Biology 2004-2005 2004-2005 5 Half Hollow Hills High School Ms. Foglia AP Biology Alternative splicing Alternative mRNAs produced from same gene when is an intron not an intron… different segments treated as exons hard to define a gene! AP Biology 2004-2005 Domains Modular architecture of many proteins AP Biology 2004-2005 discrete functional & structural regions coded by different exons 2004-2005 6 Half Hollow Hills High School Ms. Foglia AP Biology mRNA Mature mRNA AUG UGA AP Biology 2004-2005 The “Central Dogma” flow of genetic information within a cell transcription DNA RNA translation protein replication AP Biology 2004-2005 2004-2005 7
