Chapter 12 DNA & RNA Section 12 – 5 Gene Regulation.

Chapter 12DNA & RNA

Section 12 – 5Gene Regulation

Objectives

How are lac genes turned off and on?

How are most eukaryotic genes controlled?

Gene Regulation

How Does A Cell Know?

Which Gene To Express

&

Which Gene Should Stay Silent?

Gene Regulation

When a Gene is Expressed:It Is Transcribed Into mRNA

When a Gene is Silent:It Is Not Transcribed

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

Gene Regulation

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

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

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

Gene Regulation: lac Operon

Gene Regulation: lac Operon

= Lactose

ADD LACTOSE

Gene Regulation: lac Operon

Gene Regulation: lac Operon

Key Concept:

The lac Genes Are:Turned Off By Repressors

And

Turned On By The Presence Of Lactose

lac Gene Expression

Operon Has 2 Regulatory RegionsPromoter (RNA

Polymerase Binding)

Operator (O region) Bound To A lac Repressor

lac Gene Expression

lac RepressorWhen Bound To O

Region : Prevents Binding of RNA Polymerase To Promoter

Turns The Operon “OFF”

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

Regulation Can Be:

1. Based On Repressors

2. Based On Enhancers

3. Regulated At Protein Synthesis

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

Eukaryotic Gene Regulation

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

Eukaryotic Promoters

Enhancer SequencesSeries of Short DNA SequencesMany Types

Enormous Number Of Proteins Can Bind To Enhancer SequencesMakes Eukaryote Enhancement Very

Complex

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.

Regulation & Development

hox GenesControl Organ & Tissue Development

In The EmbryoMutations Lead To Major Changes

Drosophila With Legs In Place of Antennae

Regulation & Development

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

Regulation & Development