Lecture 13 - Lecture 13 Prokaryotic Regulation of Gene...

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Unformatted text preview: Lecture 13 Prokaryotic Regulation of Gene Expression Bacteria have evolved regulatory mechanisms that couple the expression of gene products to sensor systems that detect relevant compounds/nutrients in the extracellular milieu. Bacteria can utilize, for example, a number of different types of sugarlactose, glucose, galactose and xylose. Each enters the cell via a different import channel and is metabolized by a unique set of enzymes. If a given sugar is present in the environment, the cell will activate the transcription of genes required for import and processing of that sugar, and repress or block transcription of genes in other metabolic (sugar utilization) pathways. In sum, cells must recognize environmental conditions and activate or repress transcription/expression of metabolic genes accordingly Genetic switches (protein + sequence element) provide cells with a mechanism to customize gene expression to available resources. Promoter: binding site for RNA polymerase. Activator binding sites usually lie upstream of promoter Operator : repressor binding sites, usually situated downstream of promoter Operators, like promoters, are DNA sequence elements. Activators and repressors are DNA binding proteins. Binding activity of regulatory proteins is coupled to appropriate environmental conditions through effector binding at an allosteric site , a domain within the regulatory protein distinct from the DNA binding domain. Effector binding often induces structural changes in the DNA binding domain that either facilitate or prohibit the protein-DNA interaction. Allosteric effectors are usually small molecules, such as substrates (lactose), intermediates (or end products) of metabolic pathways. Repressor protein controls the lac operon Figure 10-4 In bacterial genomes, functionally related genes are often grouped in operons; several genes transcribed from a single promoter. We will look at the lac operon as a classic example of allosteric regulation of a metabolic pathway in E. coli (Lactose) Permease: lactose specific import channel....
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This note was uploaded on 11/11/2009 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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Lecture 13 - Lecture 13 Prokaryotic Regulation of Gene...

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