1/18/2016 Regulation of Bacterial Gene Regulation of Protein Synthesis and Expression Metabolism Cell carries out an enormous number of metabolic Learning Objectives reactions,which are catalyzed by enzymes. Feedback inhibition stops enzymes that are ·Define operon already produced from performing unneeded Explain pre-transcriptional regulation reactions. of gene expression in bacteria Mechanisms of gene regulation prevent synthesis of the enzyme. Cells save energy by blocking synthesis of an unneeded protein. Genes are regulated to be active only when their products are required. 60%-80%of genes are not regulated and are Operon Model of Control expressed constantly at a fixed rate-constitutive expression Constitutively expressed genes are needed in large amounts for major life processes 1.Repression inhibits gene expression by blocking transcription of mRNA,which decreases enzyme her genes are expressed as needed. synthesis indu repressed expression usually responds to over abundance of an end- In prokaryotes this regulation is coordinated by product operons,a set of genes,all of which are regulated anabolic operons -enzymes used to synthesize an as a single unit. amino acid mediated by regulatory proteins called repressors Regulatory e -repressors block RNA polymerase from initiating transcription default for an repressible gene is ON 12 1/18/2016 12 Learnin g Objectives Regulation of Bacterial Gene Expression g j • Define operon • Explain pre-transcriptional regulation of gene expression in bacteria Regulation of Protein Synthesis and Metabolism • Cell carries out an enormous number of metabolic reactions, which are catalyzed by enzymes. • Feedback inhibition stops enzymes that are already produced from performing unneeded reactions. • Mechanisms of gene regulation prevent synthesis of nzym . the enzym e. • Cells save energy by blocking synthesis of an unneeded protein. • Genes are regulated to be active only when their products are required. • 60%- 80% of genes are not regulated and are expressed constantly at a fixed rate – constitutive expression • Constitutively expressed genes are needed in large amounts for major life processes • Other genes are expressed as needed, induced/repressed expression • In prokaryotes this regulation is coordinated by operons, a set of genes, all of which are regulated as a single unit. Two genetic control mechanisms control the production of enzymes in the cell 1. Repression inhibits gene expression b y blockin g Operon Model of Control p gp y g transcription of mRNA, which decreases enzyme synthesis - usually responds to over abundance of an end￾product - anabolic operons –enzymes used to synthesize an ami id no acid - mediated by regulatory proteins called repressors - repressors block RNA polymerase from initiating transcription - default for an repressible gene is ON