1Gene RegulatioGene RegulationnCHAPTER CHAPTER 1515

REGUREGULATIONLATION OF GENE ACTIVOF GENE ACTIVITYITY

2Gene RegulatioGene RegulationnOutlineOutline

Prokaryotic RegulationProkaryotic Regulation trp Operontrp Operon

lac Operonlac Operon

Eukaryotic RegulationEukaryotic Regulation Transcriptional ControlTranscriptional Control

Posttranscriptional ControlPosttranscriptional Control

Translational ControlTranslational Control

Posttranslational ControlPosttranslational Control

Genetic MutationsGenetic Mutations CancerCancer

3Gene RegulatioGene Regulationn

Pg 252Pg 252

Operon consist of three componentsOperon consist of three componentsPromoterPromoter­DNA sequence where RNA polymerase first DNA sequence where RNA polymerase first attachesattaches­Short segment of DNAShort segment of DNA

Structural GenesStructural Genes­One to several genes coding for enzymes of a One to several genes coding for enzymes of a metabolic pathwaymetabolic pathway­Translated simultaneously as a blockTranslated simultaneously as a block­Long segment of DNALong segment of DNA

OperatorOperator­DNA sequence where active repressor bindsDNA sequence where active repressor binds­Short segment of DNAShort segment of DNA

5The trp Operon

6Gene RegulatioGene RegulationnRepressible Operons:Repressible Operons:

The trp OperonThe trp Operon

The regulator codes for a repressor The regulator codes for a repressor

If tryptophan (an amino acid) is absent:If tryptophan (an amino acid) is absent:

Repressor is unable to attach to the operator Repressor is unable to attach to the operator (expression is normally “on”)(expression is normally “on”)

RNA polymerase binds to the promoterRNA polymerase binds to the promoter

Enzymes for synthesis of tryptophan are producedEnzymes for synthesis of tryptophan are produced

If tryptophan is present:If tryptophan is present:

Combines with repressor as corepressorCombines with repressor as corepressor

Repressor becomes functionalRepressor becomes functional

Blocks synthesis of enzymes and tryptophanBlocks synthesis of enzymes and tryptophan

7Gene RegulatioGene Regulationntrp Operon Animationstrp Operon Animations

Animation #1Animation #1

Animation #2Animation #2

8The lac Operon

9Gene RegulatioGene RegulationnInducible Operons:Inducible Operons:

The lac OperonThe lac Operon

The regulator codes for a repressorThe regulator codes for a repressor

If lactose (a sugar that can be used for food) is If lactose (a sugar that can be used for food) is absent:absent:

Repressor attaches to the operatorRepressor attaches to the operator

Expression is normally “off”Expression is normally “off”

If lactose is present:If lactose is present:

It combines with repressor and renders it unable to It combines with repressor and renders it unable to bind to operatorbind to operator

RNA polymerase binds to the promoterRNA polymerase binds to the promoter

The three enzymes necessary for lactose catabolism The three enzymes necessary for lactose catabolism are producedare produced

10

Action of CAP

11Gene RegulatioGene RegulationnLac Operon AnimationsLac Operon Animations

Animation #1Animation #1

LacLac Operon Operon Induction & Quiz Induction & Quiz

12Gene RegulatioGene RegulationnNegative vs Positive ControlNegative vs Positive Control

1.1. Negative ControlNegative Control - Active - Active repressors repressors shut downshut down activity of activity of an operonan operon

2.2. Positive ControlPositive Control - when CAP - when CAP molecule is active, it molecule is active, it promotes promotes activityactivity of operon. of operon.

Use of both Use of both positivepositive and and negative negative controls allows cell to fine-tune its controls allows cell to fine-tune its control of metabolism.control of metabolism.

14

Five primary levels of control:

Nuclear levels

­Chromatin Packing

­Transcriptional Control

­Posttranscriptional Control

Cytoplasmic levels

­Translational Control

­Posttranslational Control

Regulation of Gene Expression:

Levels of Control in Eukaryotes

16Levels of Chromatin StructureEukaryotic DNA associated Eukaryotic DNA associated with histone proteins with histone proteins

Together make up Together make up chromatinchromatinAs seen in the interphase As seen in the interphase nucleusnucleus

17Figure 15.5c

Nucleosomes:Nucleosomes:DNA wound around balls of eight molecules of DNA wound around balls of eight molecules of histone proteinshistone proteinsLooks like beads on a stringLooks like beads on a stringEach bead a nucleosomeEach bead a nucleosome

The levels of chromatin packing The levels of chromatin packing determined by degree of nucleosome determined by degree of nucleosome coilingcoiling

18Gene RegulatioGene RegulationnChromatin PackingChromatin Packing

EuchromatinEuchromatinLoosely coiled DNALoosely coiled DNATranscriptionally activeTranscriptionally active

HeterochromatinHeterochromatinTightly packed DNATightly packed DNATranscriptionally inactiveTranscriptionally inactive

19X-Inactivation in Mammalian Females

Barr Bodies - AnimationBarr Bodies - AnimationFemales have two X chromosomes, but only one is Females have two X chromosomes, but only one is activeactiveOther is tightly packed along its entire lengthOther is tightly packed along its entire lengthInactive X chromosome is Barr bodyInactive X chromosome is Barr body

20Initiation of Transcription

Transcription controlled by

proteins called

transcription factors

Bind to Bind to enhancer DNAenhancer DNA

Regions of Regions of DNA where DNA where factors that factors that regulate regulate transcription transcription can also bindcan also bind

Always Always present in present in cell, but most cell, but most likely have to likely have to be activated be activated before they before they will bind to will bind to DNADNA

22Lampbrush Chromosomes

These chromosomes are

present in maturing amphibian egg cells and give evidence that when mRNA is being synthesized, chromosomes most likely decondense.

Each chromosome has

many loops extended from its axis (white). Many mRNA transcripts

are being made off these DNA

loops (red)

24Processing of mRNA

Transcripts

Excision of introns can varySplicing of exons can varyDetermines the type of mature transcript that leaves the nucleus

Control speed of mRNA transport from nucleus to cytoplasmWill affect the number of transcripts arriving at rough ERAnd therefore the amount of gene product realized per unit time

25Gene RegulatioGene RegulationnTranslational ControlTranslational Control

Translational Control - Determines degree to Translational Control - Determines degree to which mRNA is translated into a protein which mRNA is translated into a protein productproduct

Presence of 5Presence of 5′′ cap cap

Length of poly-A tail on 3Length of poly-A tail on 3′′ end end

Posttranslational Control - Affects the activity Posttranslational Control - Affects the activity of a protein productof a protein product

ActivationActivation

Degradation rateDegradation rate

26Gene RegulatioGene Regulationn

Post-Translational ControlPost-Translational Control•Posttranslational Control begins Posttranslational Control begins once a protein has been once a protein has been synthesizedsynthesized

Some Proteins are not immediately Some Proteins are not immediately active after synthesis.active after synthesis.

­Cleaving and recombiningCleaving and recombining

Some proteins are short-livedSome proteins are short-lived

­Degraded and Destroyed Degraded and Destroyed (Proteasomes)(Proteasomes)

27Gene RegulatioGene RegulationnEffect of Mutations onEffect of Mutations on

Protein ActivityProtein Activity

Point MutationsPoint Mutations Involve change in a single DNA Involve change in a single DNA nucleotidenucleotide

Changes one codon to a different Changes one codon to a different codoncodon

Affects on protein vary:Affects on protein vary:­NonfunctionalNonfunctional­Reduced functionalityReduced functionality­UnaffectedUnaffected

28Gene RegulatioGene RegulationnEffect of Mutations onEffect of Mutations on

Protein ActivityProtein Activity

Frameshift MutationsFrameshift MutationsOne or two nucleotides are either One or two nucleotides are either inserted or deleted from DNAinserted or deleted from DNA

Protein always rendered Protein always rendered nonfunctionalnonfunctional

Normal :Normal : THE CAT ATE THE RAT THE CAT ATE THE RATAfter deletion: THE ATA TET HER ATAfter deletion: THE ATA TET HER ATAfter insertion: THE CCA TAT ETH ERA TAfter insertion: THE CCA TAT ETH ERA T

29Point Mutation

30Androgen Insensitivity

•Female Appearance

•Male Karyotype

•Testes instead of ovaries & uterus in abdominal cavity

•Mutation – makes cells unable to respond to male sex hormone.

•The androgen receptor is ineffective

31Gene RegulatioGene RegulationnCarcinogenesisCarcinogenesis

Development of cancer involves a series of Development of cancer involves a series of mutationsmutations

Proto-oncogenesProto-oncogenes – Stimulate cell cycle – Stimulate cell cycle

Tumor suppressor genesTumor suppressor genes – inhibit cell – inhibit cell cyclecycle

Mutation in oncogene and tumor suppressor Mutation in oncogene and tumor suppressor gene:gene:

­ Stimulates cell cycle uncontrollablyStimulates cell cycle uncontrollably

­ Leads to tumor formationLeads to tumor formation

32

Carcinogenesis

33Achondroplasia andXeroderma Pigmentosum

34Gene RegulatioGene RegulationnCauses of MutationsCauses of Mutations

Replication ErrorsReplication Errors1 in 1,000,000,000 replications1 in 1,000,000,000 replicationsDNA polymeraseDNA polymerase­ Proofreads new strandsProofreads new strands

­ Generally corrects errorsGenerally corrects errors

Environmental MutagensEnvironmental MutagensCarcinogens - Mutagens that increase the Carcinogens - Mutagens that increase the chances of cancerchances of cancer­ Ultraviolet RadiationUltraviolet Radiation

­ Tobacco SmokeTobacco Smoke