Skip to main content
Pearson+ LogoPearson+ Logo
Ch. 18 - Control of Gene Expression in Bacteria
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Not the one you use?Change textbook
All textbooksFreeman 8th 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 term 'allosteric regulation': Allosteric regulation refers to the process by which a molecule binds to a site on a protein (called the allosteric site) that is distinct from the protein's active site, causing a change in the protein's shape and activity.
Identify the role of LuxR: LuxR is a protein that functions as a transcriptional regulator in the quorum sensing system of *Vibrio fischeri*. It controls the expression of genes involved in bioluminescence.
Explain the inducer molecule's role: The inducer molecule secreted by *V. fischeri* binds to the allosteric site of LuxR, causing a conformational change in the LuxR protein. This change enables LuxR to interact with DNA and activate transcription of target genes.
Clarify the significance of allosteric regulation: Allosteric regulation allows LuxR to respond to environmental signals, such as the concentration of the inducer molecule, ensuring that bioluminescence is activated only when the bacterial population density is high enough (quorum sensing).
Summarize the concept: LuxR being allosterically regulated means its activity is modulated by the binding of the inducer molecule at a site other than the active site, which alters its shape and function to enable gene regulation.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

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 function 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 enhance or inhibit its activity. In the case of LuxR, the inducer molecule alters its shape, affecting its ability to bind to DNA and regulate gene expression.
Recommended video:
Guided course
03:31
Cell Cycle Regulation

LuxR Protein

LuxR is a transcriptional regulator found in various bacteria, including Vibrio fischeri. It plays a crucial role in quorum sensing, a process that allows bacteria to communicate and coordinate behavior based on population density. LuxR binds to specific DNA sequences to activate or repress the expression of genes involved in bioluminescence and other collective behaviors.
Recommended video:
Guided course
02:50
Proteins

Inducer Molecule

An inducer molecule is a substance that initiates or enhances the expression of specific genes by binding to a regulatory protein. In the context of LuxR, the inducer secreted by V. fischeri binds to LuxR, promoting its active form. This interaction is essential for the bacteria to sense their environment and respond appropriately, such as by producing light in response to high cell density.
Recommended video:
Guided course
04:25
Inducible Operons
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.

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.

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.

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?

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?