Presentation on theme: "Ch. 18 Regulation of Gene Expression"— Presentation transcript:
1Ch. 18 Regulation of Gene Expression Objectives:LO 3.18 The student is able to describe the connection between the regulation of gene expression and observed differences between different kinds of organisms.LO 3.19 The student is able to describe the connection between the regulation of gene expression and observed differences between individuals in a population.LO 3.20 The student is able to explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function.LO 3.21 The student can use representations to describe how gene regulation influences cell products and function.LO 3.22 The student is able to explain how signal pathways mediate gene expression, including how this process can affect protein production..LO 3.23 The student can use representations to describe mechanisms of the regulation of gene expression.
218.1 Bacteria Often Respond to Environmental Change by Regulating Transcription Conserve resources 1 of 2 ways:Feedback inhibition (discussed in Ch. 8)Regulation of gene expression (discussed here)PrecursorFeedback inhibitionEnzyme 1Enzyme 2Enzyme 3Tryptophan(a)(b)Regulation of enzyme activityRegulation of enzyme productionRegulation of gene expressiontrpE genetrpD genetrpC genetrpB genetrpA gene
3Operons: The Basic Concept and Negative Gene Regulation Operator (“on/off switch”), promoter, and genes.Repressible (anabolic) operons: Always “on” until repressor is bound. (inhibited)Corepressor is like feedback inhibition (product works with repressor)Ex: tryptophan producing genesPromoterDNARegulatory genemRNAtrpR53ProteinInactive repressorRNA polymerasetrp operonGenes of operonOperatormRNA 5Start codonStop codontrpEtrpDtrpCtrpBtrpAEDCBAPolypeptide subunits that make up enzymes for tryptophan synthesis(a) Tryptophan absent, repressor inactive, operon on(b) Tryptophan present, repressor active, operon offTryptophan (corepressor)Active repressorNo RNA madeTrp operon – always on unless repressed by the repressor + tryptophan. Repressor is always available but in inactive form until tryptophan binds to it.
4Inducible (catabolic) operons are usually off but can be induced. Inducer inactivates the repressorEx: lac (lactose) operon(a) Lactose absent, repressor active, operon off(b) Lactose present, repressor inactive, operon onRegulatory genePromoterOperatorDNAlacZlacImRNA53No RNA madeRNA polymeraseActive repressorProteinlac operonlacYlacAmRNA 5Inactive repressorAllolactose (inducer)-GalactosidasePermeaseTransacetylaseLac Operon is always off unless induced by inducer. Lac repressor is active once made.
5Positive Gene Regulation Gene is always on but activator stimulates transcription.Ex: cAMPPromoterDNACAP-binding sitelacZlacIRNA polymerase binds and transcribesOperatorcAMPActive CAPInactive CAPAllolactoseInactive lac repressor(a)Lactose present, glucose scarce (cAMP level high): abundant lac mRNA synthesizedPromoterDNACAP-binding sitelacZlacIOperatorRNA polymerase less likely to bindInactive lac repressorInactive CAP(b)Lactose present, glucose present (cAMP level low): little lac mRNA synthesized
618.2 Eukaryotic Gene Expression is Regulated at Many Stages SignalNUCLEUSChromatinChromatin modification: DNA unpacking involving histone acetylation and DNA demethylationDNAGeneGene available for transcriptionRNAExonPrimary transcriptTranscriptionIntronRNA processingCapTailmRNA in nucleusTransport to cytoplasmCYTOPLASMmRNA in cytoplasmTranslationDegradation of mRNAPolypeptideProtein processing, such as cleavage and chemical modificationActive proteinDegradation of proteinTransport to cellular destinationCellular function (such as enzymatic activity, structural support)Each cell of multicellular organisms contain all genetic info; only some is expressed (differential gene expression).Each process has the potential for regulation.
7Regulation of Chromatin Structure Amino acids available for chemical modificationHistone tailsDNA double helixNucleosome (end view)(a) Histone tails protrude outward from a nucleosomeUnacetylated histonesAcetylated histones(b)Acetylation of histone tails promotes loose chromatin structure that permits transcriptionHistone Modifications: acetylation loosens chromatin easier protein access.DNA Methylation: addition of methyl group to gene turns it off.Epigenetic Inheritance: gene regulation passed on to offspring.
8Regulation of Transcription Initiation Control elements/enhancers upstream from a gene can activate or repress transcription factors to regulate gene expression.Combination of control elements and their activators.Like genes use similar control elements and activators.
9Mechanisms of Post-Transcriptional Regulation mRNA degradationAlternative RNA splicing: different intron/exons spliced together.ExonsDNATroponin T genePrimary RNA transcriptRNA splicingormRNA12345
1218.3 Noncoding RNAs Play Multiple Roles in Controlling Gene Expression Parts of DNA that make very small RNA (ncRNA) but not proteins; regulate gene expression.Bind to a complementary sequence of mRNA, blocking translation.Bind to DNA changing chromatin structuremicroRNAs (miRNA): begins as hairpinSmall interfering RNAs (siRNA): begins as double strand(a) Primary miRNA transcriptHairpinmiRNAHydrogen bondDicermiRNA- protein complexmRNA degradedTranslation blocked(b) Generation and function of miRNAs53
13Embryonic development: division differentiation morphogenesis 18.4 A Program of Differential Gene Expression Leads to the Different Cell Types in a Multicellular OrganismEmbryonic development:division differentiation morphogenesisCytoplasmic DeterminantsRNA and proteins from mom’s cell unevenly distributed giving rise to different cells during 1st divisions.(a) Cytoplasmic determinants in the eggUnfertilized eggSpermFertilizationZygote (fertilized egg)Mitotic cell divisionTwo-celled embryoNucleusMolecules of two different cytoplasmic determinants
14Morphogens (proteins) establish an embryo’s axes Induction is how embryonic cells effect one another due to cell-surface molecules or growth factors.Determination due to the expression of genes for tissue-specific proteins.Pattern Formation puts determined cells in their “proper places” for the resulting organism.Morphogens (proteins) establish an embryo’s axes(b) Induction by nearby cellsEarly embryo (32 cells)NUCLEUSSignal transduction pathwaySignal receptorSignaling molecule (inducer)