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 Regulation Gene 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 dif cult 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 speci c tasks saves energy allows for speci city and variation allows for body s 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 uctuations 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 polymerase s 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 speci c 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 operon s 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 can t 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 additional levels in Eukaryotes A lot of DNA contained in eukaryotes especially in comparison to prokaryotes Each cell contains same genome or library but are able to access the information in Differential Gene Expression the expression of different genes by cells with different ways the same genomes allows for genetic variation The processes