17 - Transcription (Prokaryotes); E.coli Polymerase & Promoters

17 - Transcription (Prokaryotes); E.coli Polymerase & Promoters

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1 Transcription: Prokaryotes Learning Objectives • Define levels of control of gene expression • Define transcriptional machinery • Discuss the organization of bacterial genes • Describe the process of promoter recognition by E. coli RNAP including the role of specific subunits and the cis -elements that are involved • Explain the factors that affect the strength of a promoter E. coli RNA polymerase
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2 Gene expression Process in which information carried by a gene is converted into observable product Transcription First step in gene expression - process where one strand of a DNA molecule is used as a template for synthesis of a complementary RNA, mRNA, which carries information for a specific protein = RNA like =coding =sense
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3 1cell system (Bacteria): Has to survive and reproduce Gene expression regulation - to adjust to changes in its nutritional environment - to enable cell growth and cell division Multi-cellular organism: Has to survive and reproduce but also to grow and develop; different parts of the body – different function Gene expression regulation during: Development (time) Tissue differentiation (space and “space/time combo”) Stress (as a response to environmental stress- induction) Gene expression and changes in gene expression are controlled - regulated
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4 Prokaryotes: transcription initiation is controlled •transcription and translation occur in the same compartment Regulation of Gene Expression: Pro •mRNA is polycistronic, without introns and has short half-life
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5 Regulation of Gene Expression: Eu Gene expression can be regulated at various levels in Eukaryotes In Eu, transcription initiation is most important level of regulation as well
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6 Transcription (general) Similar process to DNA synthesis Enzyme – multisubunit complex Enzyme produces nucleotide strand in 5’ to 3’ direction Mg 2+ is a co-factor (necessary to add to buffers for in vitro transcription) Both DNA strands could be templates for RNA synthesis
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7 genes a, d, e genes b, c, f, g
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8 However, there are some important differences: Enzyme is RNA polymerase (RNAP) RNAP does not require a primer Promoter sequences (binding sites for RNAP) are
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17 - Transcription (Prokaryotes); E.coli Polymerase & Promoters

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