What is the lac operon? What is the lac operon? How is it controlled?How is it controlled?

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Section 11-1Section 11-1

Control of Gene Expression Control of Gene Expression

Gene ExpressionGene Expression

Only some genes are expressed at Only some genes are expressed at any given timeany given time• Cell specializationCell specialization

Two steps:Two steps:• Transcription – regulatory sitesTranscription – regulatory sites• TranslationTranslation

The Lac OperonThe Lac Operon

Jacob and MonodJacob and Monod Studied gene expression in Studied gene expression in lac lac

operonoperon of of E. ColiE. Coli• Structural genesStructural genes• PromoterPromoter• OperatorOperator• OperonOperon

Controlling the Lac OperonControlling the Lac Operon

RepressionRepression• Repressor proteinRepressor protein• Regulator geneRegulator gene

ActivationActivation• InducerInducer

Gene Expression in EukaryotesGene Expression in Eukaryotes

Challenges:Challenges:• Larger genomeLarger genome• Several chromosomesSeveral chromosomes• Specialized cellsSpecialized cells• No operonsNo operons

How are genes controlled in How are genes controlled in eukaryotic organisms?eukaryotic organisms?

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Structure of Eukaryotic GenesStructure of Eukaryotic Genes

Control before and after transcriptionControl before and after transcription DNA is coiled – affects gene DNA is coiled – affects gene

expressionexpression• EuchromatinEuchromatin• HeterochromatinHeterochromatin

Introns-ExonsIntrons-Exons• Options for producing different proteinsOptions for producing different proteins• Role for introns?Role for introns?

More on expressionMore on expression

Control after transcriptionControl after transcription• LocationsLocations• Pre-mRNAPre-mRNA

Splicing mRNA exons – SpliceosomesSplicing mRNA exons – Spliceosomes Alternative splicingAlternative splicing RNA as enzymes – ribozymesRNA as enzymes – ribozymes

Enhancer controlEnhancer control• Enhancer regionEnhancer region• Transcription factorsTranscription factors

Chapter 11Removal of Introns After Removal of Introns After TranscriptionTranscription

Section 1 Control of Gene Expression

Chapter 11Controlling Transcription in Controlling Transcription in EukaryotesEukaryotes

Section 1 Control of Gene Expression

How do complex How do complex multicellular organisms multicellular organisms

develop from an embryo?develop from an embryo?

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Section 11-2Section 11-2

Gene Expression and Gene Expression and DevelopmentDevelopment

Cell DifferentiationCell Differentiation

MorphogenesisMorphogenesis Homeotic (Hox) genesHomeotic (Hox) genes

• Homeobox – 180 base pairsHomeobox – 180 base pairs Regulatory proteins – turn genes Regulatory proteins – turn genes

on/offon/off Similar sequences found in many Similar sequences found in many

eukaryotic organismseukaryotic organisms

CancerCancer

TumorTumor• Benign tumorBenign tumor• Malignant tumorMalignant tumor

TypesTypes• CarcinomasCarcinomas• SarcomasSarcomas• LymphomasLymphomas• LeukemiaLeukemia

The Cell CycleThe Cell Cycle

Normal – Cell needs:Normal – Cell needs:• Adequate nutritionAdequate nutrition• Attached to other cells, membrane, Attached to other cells, membrane,

fibersfibers• Stop dividing when become crowdedStop dividing when become crowded

Cancer-causing AgentsCancer-causing Agents• Growth factors and mutationsGrowth factors and mutations• CarcinogensCarcinogens• MutagensMutagens

More CausesMore Causes• Genetic factorsGenetic factors• Environmental factorsEnvironmental factors

Cigarette smokeCigarette smoke Air and water pollutionAir and water pollution UV radiationUV radiation Viral infectionViral infection

PreventionPrevention• Dietary methodsDietary methods• Behavior modificationBehavior modification

More on Causes: GenesMore on Causes: Genes

Oncogenes/Proto-oncogenesOncogenes/Proto-oncogenes Tumor-suppressor genesTumor-suppressor genes

• See Fig. 11-10, p. 214See Fig. 11-10, p. 214 VirusesViruses

Chapter 11

Effect of Mutation on Gene Effect of Mutation on Gene ExpressionExpression

Section 2 Gene Expression in Development and Cell Division

Fig. 3.23Fig. 3.23

Stem Cells - PropertiesStem Cells - Properties

Undifferentiated (unspecialized) cellsUndifferentiated (unspecialized) cells• Differentiate to any type of cell based on Differentiate to any type of cell based on

signalssignals Depending on potencyDepending on potency

Self-renewingSelf-renewing• Mitosis Mitosis differentiated cell + another differentiated cell + another

stem cellstem cell

Potency of Stem CellsPotency of Stem Cells

TotipotentTotipotent• ZygoteZygote

PluripotentPluripotent• EmbryonicEmbryonic

MultipotentMultipotent• AdultAdult

Sources of stem cellsSources of stem cells

EmbryonicEmbryonic• From blastula stage of developing From blastula stage of developing

embryo (within first approx. 2 weeks)embryo (within first approx. 2 weeks)• PluripotentPluripotent

AdultAdult• Only in certain tissues (Brain, Bone Only in certain tissues (Brain, Bone

marrow)marrow)• MultipotentMultipotent

Induced Pluripotent Stem Cells (IPS)Induced Pluripotent Stem Cells (IPS)• Somatic cell Somatic cell Pluripotent Pluripotent

Uses and HurdlesUses and Hurdles Potential Uses:Potential Uses:

• Cure diseasesCure diseases• Repair spinal injuries/brain injuriesRepair spinal injuries/brain injuries• Cloning organsCloning organs

Hurdles:Hurdles:• Signals Signals

Turning genes on/off is essentialTurning genes on/off is essential

• CulturingCulturing• Maintaining linesMaintaining lines• Moral/Ethical debateMoral/Ethical debate