Gene Regulation Lac Operon. Eukaryotes use four primary ways to control the expression of genes....
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Transcript of Gene Regulation Lac Operon. Eukaryotes use four primary ways to control the expression of genes....
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Gene Regulation
Lac Operon
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Eukaryotes use four primary ways to control the expression of genes.
• Transcriptional control – selection of genes to be transcribed and the rate of
transcription • Posttranscriptional control
– processing of mRNA and the rate at which mRNA leaves the nucleus.
• Translational control – how long mRNA remains in the cytoplasm
• Posttranslational control – additional processing that proteins require to be
functional or through feedback inhibition.
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Oncogenes
• Genes that are responsible for signaling cells to divide - called proto-oncogenes
• When damaged cause uncontrolled cell division
• Carcinogen– Agents that cause cancer
(mutations)– include radiation, cigarette
smoke, and viruses
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Normal Cells:Controlled growthContact inhibitionOne organized layerDifferentiated cells
Cancer Cells:Uncontrolled growthNo contact inhibitionDisorganized, multilayeredNondifferentiated cellsAbnormal nuclei
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Mutagens• Spontaneous
– Alkylation– Oxidation– Etc
• Radiation– UV– Gamma, Beta, Alpha– Etc
• Chemical– Base analogue– Intercalating agents– Etc
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Mutations
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Gene Regulation in Prokaryotes
• In prokaryotes, genes must also be turned on and off.
• If genes are always expressed, then much energy is wasted. The organism will quickly become lethargic and very tired.
• An Operon consists of:– structural genes– promoter – Operator– Regulatory genes– Repressor and activator proteins
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Repressible Operon - trp• repressible operon is ON by default. • regulatory genes produce inactive repressors. • end product of the pathway, tryptophan, interacts with the
inactive repressor (acting as a co-repressor), and causes a conformational change in the repressor.
• The active repressor is now able to bond to the operator and switch off transcription.
• Typical of anabolic pathways• http://bcs.whfreeman.com/thelifewire/content/chp13/13020
02.html• http://www.as.wvu.edu/~dray/219files/TrpAttenuation.mov
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Inducible Operon - lac
Negative Regulation• Regulatory gene produces repressor• Repressor is bound to the Operator• Allolactose will bond to repressor protein• Repressor will be removed Operator• RNA polymerase can transcribe• http://bcs.whfreeman.com/thelifewire/content/chp
13/1302001.html• http://www.as.wvu.edu/~dray/219files/LacOperon.
mov
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Lactose metabolism in E. coli
1. Transport lactose into the cell2. Break down lactose into glucose and
galactose
galactose glucose
lactoseGalactoside permease
E. Coli cell
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Lactose metabolism in E. coli
• The enzyme Beta-galactosidase breaks down lactose into glucose and galactose
+Beta-galactosidase
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Lac Operon Genes
• Operon: a group of genes that are commonly regulated and transcribed into mRNA
Name of the Gene Protein Product of the Gene
Lac I Gene Produces a Repressor Protein
Lac Z Gene Produces Beta-Galactosidase
Lac Y Gene Produces Galactoside Permease
Lac A Gene Produces Transacetylase
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Role of lactose
• Lactose is called an inducer molecule because it signals the production of:
(a)Beta-galactosidase: the enzyme that cleaves lactose into glucose and galactose
(b)Galactoside permease: the transport protein that allows lactose to enter a cell
(c)Transacetylase: don’t worry about this one