PowerPoint Presentation On Gene Regulation

PPT On Molecular Mechanisms Of Gene Regulation

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Gene Regulation Presentation Transcript:

1. Transcription Regulation:
Prokaryotes Transcription regulation is common mechanism in prokaryotes Negative Regulation = repressor binds to regulatory site to block transcription of active gene Positive Regulation = Activator binds to regulatory site to stimulate transcription; gene is off in absence of activator

2. Operon Model of Regulation
The operon consists of several structural genes required for lactose metabolism under the control of a single regulatory domain = coordinate regulation Repressor binding site = operator Site for transcriptional activation = promoter

3. Operon Model of Regulation
Inducible operon is activated by small molecule inducers; mode of regulation in degradative (catabolic) pathways Repressible operon is shut off by small molecule co-repressors; mode of regulation in biosynthetic (anabolic) pathways

4. Gene Regulation Mechanisms
Negative regulation: repressor protein blocks transcription: Inducible: inducer antagonizes repressor to allow transcription initiation Repressible: aporepessor combines with co-repressor to form functional repressor

5. Gene Regulation Mechanisms
Positive Regulation: transcription occurs only if promoter is activated by transcriptional activator Negative regulation is more common in prokaryotes Positive regulation is more common in eukaryotes Autoregulation: protein regulates its own transcription

 6. Lac Operon
Lactose degradation is regulated by the lactose (lac) operon The first regulatory mutations discovered affect lactose metabolism Structural proteins of the lac operon: B- galactosidase required for lactose metabolism and lactose permease required for lactose entry

7. Lac Operon
Lac operon gene expression can be inducible or constitutive The repressor is expressed constitutively (continuously) from the i gene and binds to the operator to block transcription The operon is inducible since lactose binds and inactivates the repressor to permit transcription initiation

8. Lac Operon
Lactose operator is essential site for repression Operator mutations are cis-dominant because only genes on the same genetic unit are affected Lactose promoter is essential site for transcription Lac operon contains linked structural genes and regulatory sites

9. Lac Operon
Lactose operon is also subject to positive regulation Positive regulation of the lac operon involves cAMP-CRP ( cyclic AMP receptor protein) which binds to the promoter to activate transcription by RNA polymerase cAMP-CRP complex regulates the activity of the lac operon

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