BIO311C_F08_Gene regulation

BIO311C_F08_Gene regulation - Gene regulation in bacteria...

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Gene regulation in bacteria Pages 351-356
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Constitutive expression Always “turned on” Regulated expression Turned off till needed by cell
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Studies of Studies of E. coli E. coli metabolism metabolism E. coli - only 5% transcribed at any one time GENE EXPRESSION is regulated - genes are activated (turned on) when needed and repressed (turned off) when not needed
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Operons: The Basic Concept A cluster of functionally related genes can be under coordinated control by a single on-off “switch” The regulatory “switch” is a segment of DNA called an operator usually positioned within the promoter An operon is the entire stretch of DNA that includes the operator, the promoter, and the genes that they control
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Role of regulatory proteins in transcription regulation Role of regulatory proteins in transcription regulation “Turns on” “Turns off”
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Two types of Negative regulation: Inducible Gene off (by repressor), until turned on – by inducer Repressible Gene is always turned on, until turned off by a repressor
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An inducible operon… Lac operon: Example of both Positive and Negative regulation Negative regulation: Uses a repressor protein which prevents RNAP to transcribe Positive regulation: Uses an activator protein which helps RNAP to begin transcription
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Lactose utilization in E. coli An ideal system for studying gene regulation
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Lactose utilization genes in Lactose utilization genes in E. coli E. coli lac Y lac Y – encodes permease – encodes permease lac A lac A – encodes an enzyme that adds an acetyl (CH – encodes an enzyme that adds an acetyl (CH 3 CO) CO) group to lactose group to lactose lac Z lac Z encodes encodes β β - galactosidase - galactosidase Z Y A
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Operator: Operator: ( lac O ) or O “controlling site” - bind repressor molecule with in promoter or between promoter and structural genes lac Repressor gene lac Repressor gene ( lac I ) or I makes repressor protein own promoter and terminator
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BIO311C_F08_Gene regulation - Gene regulation in bacteria...

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