BIOL1107: Test 4[ GENE REGULATION: Ch18 pp.351-366 & SciAm Article “Price of Silent Mutations”][ CELL COMMUNICATION: Ch11 (use study guide to guide reading) & Homework ] [ MITOSIS: Ch12 pp.228-237 ][ MEIOSIS: Ch13 ] [ MENDELIAN GENETICS: Ch14 ]CHAPTER 18: Gene RegulationGene Regulation: Prokaryotes & Eukaryotes must alter their patterns of gene expression in response to changes in their environmental conditions. Gene regulation is crucial to all life. Genes can constantly be turned “on/off” or expressed differently in order to have varying results in our body.- Eukaryotes (multicellular) must also develop and maintain multiple cell types; making gene regulation more difficult in Eukaryotes. - Each cell type contains same genome but must express a different subset of genes, which is a challenge of in gene regulation.18.1[Bacteria: Gene Regulation]Bacteria often respond to environment change by regulating Transcription.- Each bacterial cell has same “library” or genome, about 20,000-25,000 genes. All cells can use this same library, with different cells expressing different proteins according to their own specific tasks.- saves energy- allows for specificity and variation- allows for bodyʼs constantly changing environment- Bacteria want to conserve energy and resources; so bacteria only express genes whose products are needed by the cells.-[e.g.] E-coli bacteria need amino acid tryptophan, depending on environment of body (after rich meal, starvation, etc.). The E-coli bacteria can activate or turn off metabolic pathway that makes tryptophan.- [e.g.] Digestive enzymes are not turned on before you eat, but are after. Bacterial cells control metabolism or production of enzymes on 2 levels.- Basic mechanism for control of gene expression in bacteria = Operon Model- “Cells can adjust the activities of the enzymes already present”- “negative feedback”- allows cells to adapt to short term fluctuations in how much supply of a substance it needs. - Rapid response- “Cells can adjust the production level of certain enzymes by regulating the expression of the genes that encode the enzymes.”- occurs at level of transcription- or synthesis or mRNA.Operons: The Basic Concept- Operon Model is the basic mechanism for gene expression in bacteria- A single promoter is used for all 5 genes that are needed for the synthesis of Trp. - together the promoter and genes make a Transcription unit.- product of transcription is one long mRNA strand that can be broken into 5 separate polypeptide subunits that make up the enzymes for Trp synthesis.- (promoter is site where RNA pol can bind to DNA to being transcription)- Advantages of grouping genes into Transcription unit:- a single “on/off” switch can control the expression of the whole cluster of functionally related genes, under coordinate control. (diff. in eukaryotes)Ex. “Trp- Tryptophan- Operon”.... (example of an operon in E-coli)- The Operator (segment of DNA) is this switch.- located within promoter or between promoter and enzyme-coding regions.- controls RNA polymeraseʼs access to DNA/genes.- The Operon (trp Operon) is collectively the operator, promoter, and genes they control; the entire stretch of DNA needed to make enzymes for Trp synthesis.- so when E-coli needs to make Trp because none is present in the body from diet, all of the needed enzymes for synthesis are produced at once.- The Repressor (trp Repressor)binds to the operator, causing the Trp Operon to shut off as it blocks RNA pol from attaching to the promoter on the DNA strand. Stops production of this gene. - repressors are specific as to which operator they bind to, they can recognize distinct shapes in order to bind correctly.- trp Repressor is made by a regulatory gene (trpR).- The trp repressor is activated when Trp (tryptophan) binds to it (at an allosteric site), then the repressor binds to the operator, turning off the genes that are a part of Trp production.- Trp functions as the co-repressor, or the molecule that aids or turns on the repressor.Negative Gene Regulation- Repressible Operons/Genes: gene is active by itself already; so to regulate this gene, you must turn it off using a protein, or repressor. [e.g. Trp Operon] where trp repressor is turned off on its own.- Repressible genes use Repressor & Co-Repressor- Repressor: binds to gene inactivating it, causing it not to be expressed.- Co-repressor: molecule that turns on repressor. (Trp acts as this)- Inducible Operons/Genes: gene usually turned off; can be induced when a molecule turns repressor off. [e.g. Lac Operon] where repressor is turned on already.- Inducer: molecule that turns repressor off.- allolactose (isomer of lactose) or lactose- In the absence of lactose in the Lac Operon (which breaks down lactose), the repressor protein (lac repressor) is in its active form.Positive Gene Regulation* Lac Operon only uses lactose as a source of energy when lactose is present, and glucose is NOT present --> (meaning cAMP levels are higher).- gene normally turned off; but needs to be turned on. - RNA pol has a hard time recognizing sequence to activate or turning on the gene. - Activator: protein than binds to DNA and stimulates the transcription of a gene. (CAP) ...which also affects expression of more than 100 other genes.- Co-activator: molecule that binds to activator and turns it on. (cAMP)- Once cAMP binds to CAP protein, CAP attaches to promoter of lac operon. - allows RNA pol to attach to DNA/gene and increases the rate of transcription or begin transcription.**Lac Operon is under Dual Control- The Lac operon is under negative & positive control.- Negative control by the lac repressor, positive control by the activator CAP.- Neg: The state of the lac repressor determines whether or not transcription of the lac operonʼs genes occurs at all.- Pos: The state of the activator determines the rate of transcription.- So lac operon has “on/off switch” and “volume knob.”- The ability for a cell to catabolize other molecules such as lactose, allows cells to survive in the absence of glucose.! [e.g. If bacteria canʼt make the lacL repressor protein, this bacteria can express the lac operon in ! which of the following conditions?! ! C. Whether lactose is present or not... because no repressor is part of this operon, and ! ! lactose is only used to bind to the repressor in order for it to be released from the ! ! promoter.18.2 [Eukaryotes: Gene Expression]- Regulation occurs at many