L17 - DNA Transcription Topics DNA Transcription Different...

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Unformatted text preview: DNA Transcription Topics DNA Transcription -- Different RNA Types RNA Polymerase (Structure & Function) Messenger RNA Polycistronic operons DNA Transcription Promotors and Terminators Antisense RNA or iRNA 1 The Important (Exam) Stuff Describe the role and amount of each type of bacterial RNA. Explain where transcription occurs in the prokaryotic cell. Explain the structure of RNA polymerase and the function of sigma factor (s). Describe messenger RNA promoter, coding and terminator sequences Explain polycistronic operon structure and why polycistronic mRNA is unique to microbes. Describe two types of transcription termination. Explain the action of antisense RNA (iRNA) on transcription. The Central Dogma (Again) 2 Different Types of RNA Types of RNA RNA Typ e Abbreviation Messenger mRNA Types/cell >4,000 ? Role Information genetic % total RNA 10% Transfer tRNA ~60 functional Information 20% Ribosomal rRNA 3 (5S,16S,23S) structural Catalytic 70% Antisense iRNA ?? Inhibition <1% 3 Genes and Proteins Prokaryotic transcription is localized on cytoplasmic loops of DNA radioactive localization via exposure of film peptidoglycan 4 Overview of Transcription RNA is synthesized 5' to 3' RNA Polymerase E. coli RNAP enzyme is large (480,000 da) (a,b,b' & s subunits) Core enzyme (a b & b') is active 2 sfactor subunit binds DNA to assist in gene recognition Utilizes ATP, GTP, UTP and CTP Starts RNA polymerization without primers (unlike DNA polymerase III) DNA passes through cleft formed from combined RNAP subunits Produces ~50 bases/second 5 DNA Promoter sequences RNA polymerase s-factor 35 and 10 (Pribnow box) are consensus DNA promoter sequences. 1 2 3 4 6 Polycistronic operon Prokaryotic genes regularly encode more than one protein. Polycistronic mRNA 7 Rho dependent Termination Rho independent Termination 8 Antisense RNA or iRNA Photomicrograph of Mycobacterium smegmatis culture after 24 hours growth Photomicrograph of Mycobacterium smegmatis culture expressing antisense ftsZ gene after 24 hours growth. Text References th Pages 188192 (11 Edition) 9 ...
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