Download - Regulating Gene Expression
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Regulating Gene Expression
Turning Genes On and Off
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Procaryotes
Procaryotes are bacteria and blue green algae
They have no nucleus They have circular chromosomes made only
of DNA
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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
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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
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Lac Operon
RNA Polymerase Binding Site (Promoter)
Repressor Binding Site (Operator)
Genes coding forLactase
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Lac Operon
RNA Polymerase Binding Site (Promoter)
Genes coding forLactase
RNA Polymerase
Transcription of lactase can start when theRNA polymerase attaches to the DNA
RNA Polymerase can only attach at the binding site
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Transcription of Lactase Genes
Genes coding forLactase
RNA Polymerase
mRNA that codes for Lactase
If Lactose is present, then the bacteria will transcribe the lactase genes that will make the enzyme to digest lactose
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Lac Operon
Usually the sugar lactose is not present The genes for Lactase should be turned off
most of the time
RNA Polymerase Binding Site
Repressor Binding Site
Genes coding forLactase
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Lac Operon
Genes are turned off by blocking transcription
RNA Polymerase Binding Site
Repressor Binding Site
Genes coding forLactase
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Lac Operon
The presence of a repressor protein blocks the RNA polymerase binding site
RNA Polymerase Binding Site
Repressor Binding Site
Genes coding forLactase
RNA Polymerase
Repressor Protein blocks RNA polymerase
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Lac Operon
Lactose can act as an Inducer by deactivating the repressor protein
RNA Polymerase can now bind
Genes coding forLactase can now beTranscribed
RNA Polymerase
Deactivated Repressor ProteinInducer (lactose)
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Transcription of Lactase Genes
Genes coding forLactase
RNA Polymerase
mRNA that codes for Lactase
If Lactose is present, then the bacteria will transcribe the lactase genes that will make the enzyme to digest lactose
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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.
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Operon – a group of genes and its control mechanismPromoter- RNA polymerase binding siteOperator- Repressor protein binding siteRepressor- when active can bind to operator to block RNA polymerase (turns OFF transcription)Lac genes- genes to digest lactoseLactose- milk sugar also the inducerInducer- deactivates repressor and turns ON transcription.
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Regulatory sites
Promoter(RNA polymerase binding site)
Start transcription
DNA strand
Stop transcription
Typical Gene StructureSection 12-5
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Eukaryotic Gene Regulation
Promoter- RNA polymerase binding siteEnhancers- DNA binding site for transcription factorsTranscription factors – can help or hinder RNA polymerase from binding to the promoter, can help to unwind chromatin to allow access to DNATATA box – helps position RNA polymerase by marking beginning of transcriptionIntrons- non-coding sections of DNAExons- codes for proteins
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Transcription factors (TF)
TF can bind to the TATA box and help the RNA Polymerase (POL) to bind to the promoter to start transcription.
TF can also hinder transcription – hence they can control genes.
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Enhancers
In eukaryotic cells, enhancer regions of the DNA help transcription
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Enhancers
Factors bound to an enhancer region of DNA help to bind initiation factors that activate the RNA polymerase.
RNA Polymerase
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Enhancers
If an enhancer allows the RNA polymerase to bind more easily - more transcription will take place
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RNA Interference
RNA interference produces molecules that will breakdown mRNA, thus silencing the expression of a gene
miRNA
Silencing complex
video
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Homeotic Genes
Master control genes that regulates the development of groups of organs in specific parts of the body
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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.
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HOX genesHOX genes determine basic body plan.come from a common ancestorHOX genes-a cluster of homeobox genes that control the differentiation of cells and tissue in each segment of the embryo – determines where body parts go.Differentiation – cells become specialized during developmentIn eukaryotes only specific genes are turned on to control differentiation