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Ch. 18 - Control of Gene Expression in Bacteria
Freeman - Biological Science 7th Edition
Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook
All textbooksFreeman 7th EditionCh. 18 - Control of Gene Expression in BacteriaProblem 14
Chapter 18, Problem 14

LuxR is allosterically regulated by the inducer molecule secreted by V. fischeri. What does it mean that LuxR is allosterically regulated?

Verified step by step guidance
1
Understand the concept of allosteric regulation: Allosteric regulation occurs when a protein's function at one site is affected by the binding of a regulatory molecule to a separate site. This can result in either inhibition or activation of the protein's activity.
Identify the protein and the regulator: In this case, LuxR is the protein that is being regulated, and the inducer molecule secreted by V. fischeri acts as the regulatory molecule.
Recognize the effect of the inducer on LuxR: When the inducer molecule binds to LuxR, it causes a change in the shape or conformation of LuxR. This change can alter the activity of LuxR, typically enhancing its ability to bind to DNA and regulate gene expression.
Connect to the biological function: LuxR is involved in the regulation of bioluminescence in V. fischeri. By being allosterically regulated by the inducer molecule, LuxR can effectively control the expression of genes responsible for light production in response to environmental signals.
Consider the broader implications: Allosteric regulation is a common method of control in many biological systems, allowing for fine-tuned responses to changes in the environment or cellular conditions. Understanding this concept helps in comprehending how complex biological processes are regulated at the molecular level.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Allosteric Regulation

Allosteric regulation refers to the modulation of a protein's activity through the binding of an effector molecule at a site other than the active site. This binding induces a conformational change in the protein, which can either enhance or inhibit its function. In the case of LuxR, the inducer molecule alters its shape, affecting its ability to bind to DNA and regulate gene expression.
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Inducer Molecule

An inducer molecule is a substance that initiates or enhances the expression of specific genes by binding to regulatory proteins. In the context of LuxR, the inducer secreted by V. fischeri binds to LuxR, promoting its active form. This interaction is crucial for the regulation of bioluminescence in response to environmental signals.
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LuxR Protein

LuxR is a transcriptional regulator found in certain bacteria, including Vibrio fischeri, that plays a key role in quorum sensing. It binds to specific DNA sequences to control the expression of genes involved in bioluminescence. The allosteric regulation of LuxR by an inducer molecule allows the bacteria to coordinate their behavior based on population density, enhancing survival and communication.
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Related Practice
Textbook Question

The Hawaiian bobtail squid (Euprymna scolopes) is able to glow from luminescent Vibrio fischeri bacteria held in its light organs. As it swims at night near the ocean surface, it adjusts the amount of light visible to predators below to match the light from the stars and moon. Predators have difficulty seeing the illuminated squid against the night sky.

The bacteria glow in response to a molecule that regulates expression of genes involved in light-producing chemical reactions. The regulator controls production of the genes' mRNA. Therefore, the light-producing genes are under

a. Transcriptional control.

b. Translational control.

c. Post-translational control.

d. Negative control.

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Textbook Question
The light-producing genes of V. fischeri are organized in an operon that is under positive control by an activator protein called LuxR. Would you expect the genes of this operon to be transcribed when LuxR is bound or not bound to a DNA regulatory sequence? Explain.
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Textbook Question
The diagram shown here is a model of the gene regulatory circuit for light production by V. fischeri cells. The lux operon contains genes for luminescence (luxCDABE) and a gene, luxI, that encodes an enzyme that catalyzes the production of an inducer. This inducer easily moves back and forth across the plasma membrane and acts as a signaling molecule. The lux operon is never completely turned off. The luxR gene codes for the activator LuxR. The inducer can bind to LuxR, and when it does, the LuxR–inducer complex can bind to a regulatory site to activate transcription of the lux operon and inhibit transcription of luxR. Explain how this gene regulatory circuit accounts for bacteria emitting light only when they reach a high cell density.
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Textbook Question
What characteristic of the light-producing regulatory circuit is consistent with the idea that it may be a regulon? What characteristic of this circuit stretches the definition for a regulon?
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Textbook Question
Quorum sensing (introduced in Ch. 11, Section 11.4) allows bacteria to detect the number of neighboring cells and to trigger a response only when this number reaches a critical level. Quorum sensing is used by V. fischeri in light production and by many pathogenic bacteria, including Vibrio cholerae, to turn on genes for toxin production only when a critical cell density is reached. Why might quorum sensing be beneficial to pathogenic bacteria?
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