Chapter 12 DNA & RNA Section 12 – 5 Gene Regulation.
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Transcript of Chapter 12 DNA & RNA Section 12 – 5 Gene Regulation.
![Page 1: Chapter 12 DNA & RNA Section 12 – 5 Gene Regulation.](https://reader030.fdocuments.us/reader030/viewer/2022020117/56649d195503460f949ee7fb/html5/thumbnails/1.jpg)
Chapter 12DNA & RNA
Section 12 – 5Gene Regulation
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Objectives
How are lac genes turned off and on?
How are most eukaryotic genes controlled?
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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 ByPromoters
RNA Polymerase Binding Sites Certain DNA Base Pair Sequences
Start & Stop Base Pair SequencesRegulatory Sites
DNA Binding Proteins Regulate Transcription
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Gene Regulation
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Gene Regulation: lac 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
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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:1. Transport Lactose Across Cell Membrane
2. Separate The Two Sugars
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Gene Regulation: lac Operon
Each Task Requires A Specific Proteinbut
Proteins Not Needed If Glucose Present (why waste energy if you already have food?)
soGenes 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
= Lactose
ADD 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 RegionsPromoter (RNA
Polymerase Binding)
Operator (O region) Bound To A lac Repressor
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lac Gene Expression
lac RepressorWhen 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 LactoseHigher Affinity For
Lactose When Lactose Present lac
Repressor Is Released From O RegionAllows 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 UsuallyNOT 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 BoxAbout 30 Base Pairs LongFound Before Most GenesPositions RNA Polymerase
Usually TATATA or TATAAAPromoters Usually Occur Just Before
The TATA Box
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Eukaryotic Promoters
Enhancer SequencesSeries of Short DNA SequencesMany Types
Enormous Number Of Proteins Can Bind To Enhancer SequencesMakes 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 SpecializationAll Cells Have Same ChromosomesSome Liver, Skin, Muscle, etc.
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Regulation & Development
hox GenesControl Organ & Tissue Development
In The EmbryoMutations 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 EukaryotesShows Common AncestryPax 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 >600M Years Ago
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Regulation & Development