Lecture 13 Chapter 10 - Introduction to Genetic Analysis...

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    Introduction to Genetic Analysis Ninth Edition Anthony J. F. Griffiths, Susan R. Wessler, Richard C.  Lewontin, and Sean B. Carroll CHAPTER 10 Regulation of Gene Expression in Bacteria and Their Viruses Copyright 2008 © W H Freeman and Company
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    Regulation of gene expression: Important regulatory elements
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    Regulation of gene expression: Prokaryotes vs. Eukaryotes
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    Transcriptional Regulation is based on  DNA-protein interactions Regulation of transcription initiation. DNA elements    PROMOTER Proteins        RNA POLYMERASES Decision as to whether gene is going to be turned ON or  OFF. DNA element  OPERATOR Proteins ACTIVATORS, REPRESSORS.
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    Regulatory Elements: Cis acting and Trans acting Cis-acting elements   DNA elements Linked to the gene they regulate Promoters, operators Target sequences for transacting elements. Trans-acting elements Proteins Usually not linked to the gene they regulate Lac repressor Binds cis-acting elements.
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    Regulation of gene expression: 1. Positive Regulation-  1. The  binding of an activator  protein to the operator is a pre- requisite for transcription initiation. 1. Helps to recruit and tether the RNA polymerase at the promoter. 1. Negative Regulation – Lac operon 1. The  obstruction of a repressor to bind  the promoter is a pre- requisite for transcription initiation. 1. The repressor acts to  1. physically block RNA polymerase from binding the promoter  2. or  3. to impeded the movement of RNA polymerase once it is bound.
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    Regulation of gene expression: Positive & Negative Regulation
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    Regulation of gene expression: Regulatory proteins contain a DNA binding domain and an  allosteric site The allosteric site usually interacts with or responds to small  molecules ( ALLOSTERIC EFFECTORS ). Allosteric effectors  bind regulatory proteins  induces a conformational change in the protein  converts the DNA binding site from one state (functional or non- functional) to another.  
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    Regulation of gene expression: Some regulators must bind to their allosteric effector in order  activate the gene
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    Prokaryotic Gene Regulation The  lac  operon system
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Lecture 13 Chapter 10 - Introduction to Genetic Analysis...

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