DNA & RNA Gene Expression and Regulation

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

Gene Regulation When a Gene is Expressed:When a Gene is Expressed: –It Is Transcribed Into mRNA When a Gene is Silent:When a Gene is Silent: –It Is Not Transcribed

Gene Regulation Expression Regulated ByExpression Regulated By –Promoters RNA Polymerase Binding SitesRNA Polymerase Binding Sites Certain DNA Base Pair SequencesCertain DNA Base Pair Sequences –Start&StopBase Pair Sequences –Start & Stop Base Pair Sequences –Regulatory Sites DNA Binding ProteinsDNA Binding Proteins Regulate TranscriptionRegulate Transcription

Gene Regulation

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

Gene Regulation: lac Operon The lac Operon –Regulates Lactose Metabolism –It Turns On Only When Lactose Is Present & Glucose is Absent –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

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 Present But Lactose Is Present Genes Coding For Proteins Expressed Only When There Is No Glucose Present But Lactose Is Present

Gene Regulation: lac Operon

= Lactose ADDLACTOSE ADD LACTOSE

Gene Regulation: lac Operon

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

lac Gene Expression Operon Has 2 Regulatory RegionsOperon Has 2 Regulatory Regions –Promoter (RNA Polymerase Binding) –Operator (O region) Bound To A lac Repressor

lac Gene Expression lac Repressor lac Repressor –When Bound To O Region : Prevents Binding of RNA Polymerase To Promoter –Turns The Operon “OFF”

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

Regulation Can Be: 1.Based On Repressors 2.Based On Enhancers 3.Regulated At Protein Synthesis

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

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

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

Eukaryotic Promotors Some Enhance Transcription By Opening Up Packed ChromatinSome Enhance Transcription By Opening Up Packed Chromatin Others Attract RNA PolymeraseOthers Attract RNA Polymerase Some Block Access To GenesSome Block Access To Genes Key To Cell SpecializationKey To Cell Specialization –All Cells Have Same Chromosomes –Some Liver, Skin, Muscle, etc.

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

Regulation & Development

hox Genes Present In All Eukaryotes –Shows Common Ancestry – Pax 6 hox gene Controls eye growth in Drosophila, Mice & ManControls eye growth in Drosophila, Mice & Man Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue. Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue. Common Ancestor >600M Years Ago

Regulation & Development