Chapter 12 DNA

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Chapter 12DNA RNA

• Section 12 5Gene Regulation

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Gene Regulation

• How Does A Cell Know?
• Which Gene To Express
• Which Gene Should Stay Silent?

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Gene Regulation

• When a Gene is Expressed
• It Is Transcribed Into mRNA
• When a Gene is Silent
• It Is Not Transcribed

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Gene Regulation

• Expression Regulated By
• Promoters
• RNA Polymerase Binding Sites
• Certain DNA Base Pair Sequences
• Start Stop Base Pair Sequences
• Regulatory Sites
• DNA Binding Proteins
• Regulate Transcription

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Gene Regulation
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Prokaryote Gene Regulationlac Operon

• What is an Operon?
• Group of Genes That Operate Together
• For Example
• E. coli ferments lactose
• To Do That It Needs Three Enzymes (Proteins), It
  Makes Them All At Once!
• 3 Genes Turned On Off Together. This is known
  as the lac Operon (lactose Operon)

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Gene Regulation lac Operon

• The lac Operon
• Regulates Lactose Metabolism
• It Turns On Only When Lactose Is Present
  Glucose is Absent.
• Lactose is a Disaccharide
• A Combination of Galactose Glucose
• To Ferment Lactose E. coli Must
• Transport Lactose Across Cell Membrane
• Separate The Two Sugars

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Gene Regulation lac Operon

• Each Task Requires A Specific Protein
• but
• Proteins Not Needed If Glucose Present
  (why waste energy if you already have food?)
• so
• Genes Coding For Proteins Expressed Only When
  There Is No Glucose Present But Lactose Is Present

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Gene Regulation lac Operon
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Gene Regulation lac Operon
ADD LACTOSE
Lactose
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Gene Regulation lac Operon
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Gene Regulation lac Operon

• Key Concept
• The lac Genes Are
• Turned Off By Repressors
• And
• Turned On By The Presence Of Lactose

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lac Gene Expression

• Operon Has 2 Regulatory Regions
• Promoter (RNA Polymerase Binding)
• Operator (O region) Bound To A lac Repressor

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lac Gene Expression

• lac Repressor
• When Bound To O Region Prevents Binding of RNA
  Polymerase To Promoter
• Turns The Operon OFF

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lac Gene Expression

• lac Repressor Also Binds To Lactose
• Higher Affinity For Lactose
• When Lactose Present lac Repressor Is Released
  From O Region
• Allows Transcription of All Three Genes

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Regulation Can Be

1. Based On Repressors
2. Based On Enhancers
3. Regulated At Protein Synthesis

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Eukaryotic Gene Regulation

• Operons Usually
• NOT Found In Eukaryotes
• Key Concept
• Most Eukaryotic Genes Are Controlled Individually
  And Have Regulatory Sequences That Are Much More
  Complex Than Prokaryotic Gene Regulation

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Eukaryotic Gene Regulation
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Eukaryotic Gene Regulation

• TATA Box
• About 30 Base Pairs Long
• Found Before Most Genes
• Positions RNA Polymerase
• Usually TATATA or TATAAA
• Promoters Usually Occur Just Before The TATA Box

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Eukaryotic Promoters

• Enhancer Sequences
• Series of Short DNA Sequences
• Many Types
• Enormous Number Of Proteins Can Bind To Enhancer
  Sequences
• Makes Eukaryote Enhancement Very Complex

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Eukaryotic Promotors

• Some Enhance Transcription By Opening Up Packed
  Chromatin
• Others Attract RNA Polymerase
• Some Block Access To Genes
• Key To Cell Specialization
• All Cells Have Same Chromosomes
• Some Liver, Skin, Muscle, etc.

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Regulation Development

• hox Genes
• Control Organ Tissue Development In The Embryo
• Mutations Lead To Major Changes
• Drosophila With Legs In Place of Antennae

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Regulation Development
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Regulation Development

• hox Genes Present In All Eukaryotes
• Shows Common Ancestry
• Pax 6 hox gene
• Controls eye growth in Drosophila, Mice Man
• Pax 6 from Mouse Placed In Knee Development
  Sequence Of Drosophila Developed Into Eye Tissue.
• Common Ancestor gt600M Years Ago

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Regulation Development