Chapter 18: Regulation of Gene Expression – Flashcards
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Gene expression
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The set of processes, including transcription and translation, that convert information in DNA into a product of a gene, most commonly a protein
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Transcriptional control
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Regulation of gene expression by various mechanisms that change the rate at which genes are transcribed to form mRNA. In negative control, binding of a regulatory protein to DNA represses transcription; in positive control, binding of a regulatory protein to DNA promotes transcription.
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Translational control
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Regulation of gene expression by various mechanisms that alter the life span of messenger RNA or the efficiency of translation.
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Post-translational control
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Regulation of gene expression by modification of proteins after translation
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Is transcriptional control slow and efficient or fast and energetically expensive?
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Transcriptional control is slow and efficient. Post-translational control is fast and energetically expensive.
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constitutive
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Always occurring; always present.
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inducer
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A small molecule that triggers transcription of a specific gene.
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mutagens
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Any physical or chemical agent that increases the rate of mutation
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replica plating
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A method of identifying bacterial colonies that have certain mutations by transferring cells from each colony on a master plate to a second plate and observing their growth when exposed to different conditions.
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medium
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Any liquid or solid that supports the growth of cells
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constitutive mutants
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An abnormal strain that produces a product at all times, instead of under certain conditions only.
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Negative control
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When a regulatory protein shuts down expression by binding to DNA on or near the gene
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repressor
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(1) In bacteria, a protein that binds to an operator sequence in DNA polymerase, helicase, primase, and other enzymes. (2) In eukaryotes, a protein that binds to a silencer sequence in DNA to prevent or reduce gene transcription.
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positive control
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When a regulatory protein triggers expression by binding to DNA on or near the gene.
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activator
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A protein that binds to a DNA regulatory sequence to increase the frequency of transcription initiation by RNA polymerase
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operon
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A region of prokaryotic DNA that codes for a series of functionally related genes and is transcribed from a single promoter into one mRNA
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lac operon
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A set of three genes in E. coli that are transcribed into a single mRNA and required for lactose metabolism
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operator
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In prokaryotic DNA, a binding site for a repressor protein, located near the start of an operon.
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allosteric regulation
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Regulation of a protein's function by binding of a regulatory molecule, usually to a specific site distinct from the active site, that causes a change in the protein's shape.
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ara operon
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A set of three genes in E. coli that are transcribed into a single mRNA and required for metabolism of the sugar arabinose. Transcription of the are operon is controlled by the AraC regulatory protein.
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AraC
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Regulatory gene (araC) or regulatory protein (AraC) of the E. coli ara operon.
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Global gene regulation
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The regulation of multiple bacterial genes that are not part of one operon.
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regulon
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a set of separate genes or operons that contain the same regulatory sequences and are controlled by a single type of regulatory protein
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Replica plating is used to isolate mutants that
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cannot grow in a particular condition.
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Why are genes involved in lactose metabolism considered to be an operon?
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They are all controlled by the same promoter.
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In the lac operon, the repressor inhibits transcription when
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The repressor is not bound to the inducer.
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Activators bind to regulatory sequences in ________ and to _______ polymerase.
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DNA; RNA
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How does inducer exclusion control gene expression in the lac operon?
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When glucose and another sugar are present in the environment, inducer exclusion prevents the use of the other sugar and allows only use of glucose
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A regulon is a set of genes controlled by
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One type of regulator of transcription.
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E. coli expresses genes for glycolytic enzymes constitutively. Why?
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The glycolytic enzymes are always needed in the cell because they are required to produce ATP, and ATP is always needed.
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Explain the difference between positive and negative control over transcription.
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Positive control means that a regulatory protein, when present, causes transcription to increase. Negative control means that a regulatory protein, when present, prevents transcription.
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Predict what would happen if the lac repressor protein were altered so it could not bind inducer.
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The repressor would always be bound to DNA
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Predict what would happen to regulation of the lac operon in the lacI gene were moved 50,000 nucleotides upstream of its normal location.
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Regulation of the lac operon should be normal. The location of the lacI gene isn't important, because the gene produces a protein that diffuses within the cell to the operator.
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If any of the following hypothetical drugs could be developed, which would be most effective in preventing cholera?
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A drug that blocked the DNA-binding activity of the activator
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IPTG is a molecule with a structure very similar to lactose. IPTG can be transported into cells by galactoside permease and can bind to the lac repressor protein. However, unlike lactose, IPTG is not broken down by B-galactosidase. Predict what would occur regarding lac operon regulation if IPTG were added to E. coli growth medium containing arabinose and no glucose or lactose.
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The lac operon would be strongly induced. Once inside the cell, the IPTG will bind to the repressor, causing it to release from DNA. IPTG cannot be broken down, so its concentration will remain high. Finally, since glucose is absent, there will be no inducer exclusion to inhibit IPTG transport through galactoside permease transporter.
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What is the role of lactose in regulating lac operon expression?
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It induces transcription by binding to the repressor and causing its release from the operator.
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What is the pattern of expression of β-galactosidase in lacI— cells and why?
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Constitutive expression, because there is no repressor
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Which of these is NOT a component of the lac operon?
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regulatory gene only
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Regulatory proteins bind to _____.
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the operator
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In the presence of a regulatory protein the lac operon is _____.
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not transcribed
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Under what condition is the AraC protein an activator?
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The AraC protein is an activator when it is bound to arabinose.
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The lac repressor protein binds to the operator when it is ______.
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not bound to lactose
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Which of the following leads to the highest rate of lac operon transcription?
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high lactose levels and low glucose levels
