G2Prokaryote - Prokaryotic Gene Regulation Regulation of...

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Prokaryotic Gene Regulation Heyer 1 Regulation Regulation of Bacterial Gene Expression Figure 18.20a, b (a) Regulation of enzyme activity Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 Regulation of gene expression Feedback inhibition Tryptophan Precursor (b) Regulation of enzyme production Gene 2 Gene 1 Gene 3 Gene 4 Gene 5 Metabolic Regulation 1. 1. Adjust the activity of metabolic enzymes already present Adjust the activity of metabolic enzymes already present 2. Regulate the genes encoding the metabolic enzymes Regulate the genes encoding the metabolic enzymes Figure 18.20a, b (a) Regulation of enzyme activity Enzyme 1 Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 Regulation of gene expression Feedback inhibition Tryptophan Precursor (b) Regulation of enzyme production Gene 2 Gene 1 Gene 3 Gene 4 Gene 5 Operons : functional gene clusters • In bacteria, genes are often clustered into operons , composed of –A promoter • Site for RNA-polymerase to bind and initiate transcription –An operator , the “on-off” switch • Region of DNA within the promoter or between the promoter and the first gene –The genes for metabolic enzymes • Usually a set of enzymes catalyzing different steps in a common metabolic pathway • All the genes in the operon set are transcribed onto a single, common mRNA Operons : functional gene clusters Regulation of Bacterial Gene Expression • Conserve energy — Metabolism is precisely regulated – Make only proteins needed at a specific time • Non-regulated gene expression – RNA-poly binds freely to promoter – Constitutive genes— Enzymes always needed (e.g., glycolysis) Negative gene regulation – Repressor protein binds operator Block RNA polymerase Inhibits gene expression Decreases synthesis of enzymes Positive gene regulation
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This note was uploaded on 09/02/2011 for the course BIOL 6B taught by Professor Heyer during the Spring '10 term at DeAnza College.

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G2Prokaryote - Prokaryotic Gene Regulation Regulation of...

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