8/8 Ch 16 Notes
8/8 Ch 16 Notes 30156
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This 4 page Class Notes was uploaded by Hannah Kennedy on Saturday August 13, 2016. The Class Notes belongs to 30156 at Kent State University taught by Dr. Helen Piontkivska in Spring 2016. Since its upload, it has received 15 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
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Date Created: 08/13/16
© Hannah Kennedy, Kent State University 8/8 Lecture Notes—Ch. 16, 17, 24.4: Gene Regulation and Cancer Ch. 16—Gene Regulation in Bacteria 1. Key concepts a. Information flow in the cell leads to various mechanisms that can regulation different parts of this process b. Coordinated gene expression control—operons in prokaryotes c. Role of chromatin in eukaryotic gene expression d. Elements of eukaryotic gene expression regulation 2. Gene regulation in Prokaryotes a. Gene regulation = the phenomenon in which the level of gene expression can vary under different conditions b. Constitutive genes = unregulated genes; encode proteins that are continuously needed for the survival of the bacterium c. Key benefit: encoded proteins are produced only when they’re needed so the cell doesn’t waste energy making things it doesn’t need d. Common processes regulated at genetic level: i. Metabolism: e.g. certain enzymes are needed for bacteria to metabolize sugars ii. Response to environmental stress: protein help bacteria survive envmtal stress and are needed only when its confronted with the stress iii. Cell division 3. Prokaryotic gene regulation (goal of gene regulation is to respond to environmental stimuli in the most beneficial manner) a. Common way to regulate gene expression is by influencing the rate at which transcription is initiated (i.e. the rate of RNA synthesis can be increased or decreased) b. Types of regulation (2 different ways) i. Based on role of substrate (3 different types of genes) 1. Inducible genes = genes whose expression will be up-regulated in the presence of a certain stimuli (e.g. food) a. Inducer = small effector molecule that causes transcription to increase (by doing 2 things) i. Bind to a repressor protein and prevent it from binding to the DNA ii. Bind to an activator protein and cause it to bind to the DNA 2. Repressible genes = genes that reduce the rate of transcription; usually something from bacteria but if you have access to it in the environment you no longer need to make it on your own a. Inhibitor = binds to an activator protein and prevents it from binding to the DNA to reduce the rate of transcription 3. Housekeeping genes = genes that aren’t regulated because you make and need them; they are not in response to the environment ii. Regulation mechanism (2 kinds of regulation) 1. positive regulation: regulates an activator protein to induce transcription a. activator = a regulatory protein that increases the rate of transcription b. turning gene on via the binding mechanism 2. negative regulation: pulls off the repressor from the promoter and turns on gene regulation © Hannah Kennedy, Kent State University a. repressor = a regulatory protein that binds to the DNA and inhibits transcription b. Binding of regulatory proteins can either activate or block transcription i. Cis-acting sites (operators are regulatory regions) 1. Operator is a part of the promoter that acts as a switch for regulating whether or not RNA polymerase will move down the gene ii. Trans-acting molecules (activator, repressor) c. Small effector molecules = molecules that don’t bind directly to the DNA to alter transcription; binds to an activator or repressor and causes a conformational change c. Coordinate regulation i. Operon = section of DNA that encodes multiple genes that has a common regulatory mechanism (“master switch”); enables bacteria to have a faster response to environment 1. Eukaryotes don’t have operons common functional goal so the expression of the genes occur as a single unit 2. Encodes polycistronic RNA a. Polycistronic RNA = RNA that contains the sequences of 2 or more genes 3. Biological advantage: allows bacteria to coordinately regulate group of genes that are involved with 4. Promoter = flanks the operon and signals the beginning of transcription 5. Terminator = specifies the end of transcription d. Lactose metabolism in E. coli i. enzyme adaptation = the observation that a particular enzyme appears within a living cell only after the cell has been exposed to the substrate for it; due to transcriptional regulation of genes ii. 2 proteins necessary for lactose metabolism 1. Beta-galactosidase—cleaves middle bond of lactose into galactose and glucose; converts a small percentage of lactose into allolactose a. Allolactose is a small effector molecule that regulates the lac operon b. As allolactose rises in the cytoplasm, the allolactose binds to the lac repressor which gives a conformational change that prevents the repressor from binding to the lacO allowing transcription of lacZ, lacY, and lacA 2. Lactose permease—transports lactose into cells iii. Lactose (lac) operon 1. lacP = promoter 2. lacO = operator = sequence of bases that provides a binding site for a repressor protein © Hannah Kennedy, Kent State University 3. lacZ, lacY, lacA = structural genes a. lacY encodes lactose permease b. lacA encodes galactoside transacetylase (enzyme that modifies lactose and its analogs) 4. lacI = encodes the lac repressor a. lac repressor = a protein that is important for regulation of the lac operon 5. CAP site = catabolite activator protein = DNA sequence recognized by activator protein 6. terminator 7. Repressor gene: have 2 domains. 1 is capable of binding to DNA and the other can respond to whatever its regulating (e.g. lactose) iv. Lac operon transcriptional regulation mechanisms 1. inducible negative regulation of lac operon (2 scenarios)—involves the lac repressor protein (binds to the operator and prevents RNA polymerase from transcribing structural genes) a. when lactose is absent i. lac repressor is bound to the operator site and the structural genes are not transcribed b. when lactose is present i. binds to the repressor, a conformational change occurs in the lac repressor and it is prevented from binding to the operator site and RNA polymerase transcribes the operon v. cycle of lac operon induction and repression 1. when lactose is available, small amount of it is taken up and converted to allolactose via beta-galactosidase. 2. Allolactose binds to repressor and causes it to fall off lacO 3. Lac operon proteins are synthesized which promotes the metabolism of lactose 4. Lactose is depleted and allolactose levels decrease 5. Allolactose is released fro mthe repressor and allows it to bind to lacO 6. Proteins involved with lactose utilization are degraded e. What if gene regulation is broken i. constitutive mutants = enzymes that are produced regardless of presence or absence of lactose 1. lacI gene: regulator mutations 2. lacO gene: operator mutations (unable to interact with repressor and it is unable to block it therefore the gene will always be on) - 3. lacI: gene is on all the time therefore all structural genes will be expressed in the presence AND absence of lactose a. could be due to the operons inability to make a repressor or it could make a repressor that cnt bind to the DNA at the operator b. loss of function mutations prevent lac repressor from binding to lacO and inhibiting transcription 4. lacO : a. lacZ alleles are also present to allow lacO to work in a single DNA molecule because f. Merozygote = a partial diploid organism i. 2 important points © Hannah Kennedy, Kent State University 1. Two lacI gene- can be different alleles (e.g. lacI gene on chromosome can be lacI that causes constitutive expression and lacI gene on F’ can be normal 2. Genes on F’ factor and genes on chromosome aren’t adjacent to each other ii. Trans-effect = a form of genetic regulation that can occur even though 2 DNA segments aren’t physically adjacent: the lac repressor and activator 1. Mediated by genes that encode regulatory proteins iii. Cis-effect = a DNA segment that must be adjacent to the genes that it regulates: lacO 1. Mediated by DNA sequences that are bound by regulatory proteins