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Regulating Gene Expression

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  1. Regulating Gene Expression Turning Genes On and Off

  2. Procaryotes • Procaryotes are bacteria and blue green algae • They have no nucleus • They have circular chromosomes made only of DNA

  3. Procaryotes • On procaryotic chromosomes there are many genes • We will concentrate on how the genes that code for lactase is controlled • Lactase is the enzyme that digests the milk sugar lactose

  4. Lac Operon • The genes that code for lactase and its associated control mechanisms is called the Lac Operon. • The Lac Operon was first described by Jacob and Monod

  5. Lac Operon Genes coding for Lactase Repressor Binding Site (Operator) RNA Polymerase Binding Site (Promoter)

  6. Lac Operon Transcription of lactase can start when the RNA polymerase attaches to the DNA RNA Polymerase Genes coding for Lactase RNA Polymerase Binding Site (Promoter) RNA Polymerase can only attach at the binding site

  7. Transcription of Lactase Genes mRNA that codes for Lactase Genes coding for Lactase RNA Polymerase If Lactose is present, then the bacteria will transcribe the lactase genes that will make the enzyme to digest lactose

  8. Lac Operon • Usually the sugar lactose is not present • The genes for Lactase should be turned off most of the time Genes coding for Lactase Repressor Binding Site RNA Polymerase Binding Site

  9. Lac Operon • Genes are turned off by blocking transcription Genes coding for Lactase Repressor Binding Site RNA Polymerase Binding Site

  10. Lac Operon • The presence of a repressor protein blocks the RNA polymerase binding site RNA Polymerase Genes coding for Lactase Repressor Binding Site Repressor Protein blocks RNA polymerase RNA Polymerase Binding Site

  11. Lac Operon • Lactose can act as an Inducer by deactivating the repressor protein RNA Polymerase Genes coding for Lactase can now be Transcribed RNA Polymerase can now bind Deactivated Repressor Protein Inducer (lactose)

  12. Transcription of Lactase Genes mRNA that codes for Lactase Genes coding for Lactase RNA Polymerase If Lactose is present, then the bacteria will transcribe the lactase genes that will make the enzyme to digest lactose

  13. Online Quiz • Go to this site http://midpac.edu/~biology/Intro%20Biology/PH%20Biology%20Lab%20Simulations/lacoperon/intro.html and do the simulation • Then take the self quiz –PRINT OUT to turn in tomorrow.

  14. Operon – a group of genes and its control mechanism • Promoter- RNA polymerase binding site • Operator- Repressor protein binding site • Repressor- when active can bind to operator to block RNA polymerase (turns OFF transcription) • Lac genes- genes to digest lactose • Lactose- milk sugar also the inducer • Inducer- deactivates repressor and turns ON transcription.

  15. Typical Gene Structure Section 12-5 Promoter(RNA polymerase binding site) Regulatory sites DNA strand Start transcription Stop transcription

  16. Eukaryotic Gene Regulation • Promoter- RNA polymerase binding site • Enhancers- DNA binding site for transcription factors • Transcription factors – can help or hinder RNA polymerase from binding to the promoter, can help to unwind chromatin to allow access to DNA • TATA box – helps position RNA polymerase by marking beginning of transcription • Introns- non-coding sections of DNA • Exons- codes for proteins

  17. Transcription factors (TF) • TF can bind to the TATA box and help the RNA Polymerase (POL) to bind to the promoter to start transcription.

  18. RNA Interference miRNA • RNA interference produces molecules that will breakdown mRNA, thus silencing the expression of a gene Silencing complex video

  19. Homeotic Genes • Master control genes that regulates the development of groups of organs in specific parts of the body

  20. Homeobox genes • Within the Homeotic gene there • is a 180-base sequence which is • called the homeobox. • The homeobox gene controls for transcription factors that activate other genes that affect development and differentiation. Ex: control of wing or leg development. • These same genes are found in many different organisms – controlling the same areas of the body.

  21. HOX genes • HOX genes-a cluster of homeobox genes thatcontrol the differentiation of cells and tissue in each segment of the embryo. • Differentiation – cells become specialized during development • In eukaryotes only specific genes are turned on to control differentiation