PPP_Ch 17 - CHAPTER 17 Regulation of gene expression in...

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CHAPTER 17 Regulation of gene expression in prokaryotes Dr. Sanghamitra Mohanty
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17.1 Prokaryotes Regulate Gene Expression in Response to Environmental Conditions Gene regulation has been studied extensively in E. coli . Enzymes may be: inducible (adaptive) constitutive repressible Regulation may be under positive control or negative control .
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17.2 Lactose Metabolism in E. coli Is Regulated by an Inducible System The enzymes responsible for lactose metabolism are inducible and lactose is the inducer. Regulatory elements are almost always located upstream of the gene cluster they control and are cis -acting . The molecules that bind these cis -acting sites are trans -acting elements .
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The lac operon has three structural genes, lacZ , lacY , and lacA , with an upstream regulatory region consisting of an operator and a promoter ( Figure 17.1 ).
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The lacZ gene encodes β -galactosidase , an enzyme that converts the disaccharide lactose to the monosaccharides glucose and galactose . . The lacY gene specifies the primary structure of permease , an enzyme that facilitates the entry of lactose into the bacterial cell. The lacA gene codes for the enzyme transacetylase , which may be involved in the removal of toxic by-products of lactose digestion from the cell.
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The structural genes of the lac operon are transcribed as a polycistronic mRNA .
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Jacob and Monod proposed the operon model in which a group of genes is regulated and expressed together as a unit. The
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This note was uploaded on 07/04/2011 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas at Austin.

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PPP_Ch 17 - CHAPTER 17 Regulation of gene expression in...

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