Skip to main content
Pearson+ LogoPearson+ Logo
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 7
Chapter 18, Problem 7

Explain why it makes sense for the lexA regulatory gene of the SOS regulon to be expressed constitutively.

Verified step by step guidance
1
Understand the role of the lexA gene: The lexA gene encodes the LexA protein, which is a repressor that regulates the expression of the SOS regulon genes involved in DNA repair and cell cycle control in response to DNA damage.
Recognize the importance of constant availability: By being expressed constitutively, the LexA protein is always present in the cell. This constant availability ensures that LexA can rapidly respond to any occurrence of DNA damage by repressing or derepressing the SOS regulon genes as needed.
Consider the mechanism of action: Upon DNA damage, the RecA protein is activated and stimulates the self-cleavage of LexA, leading to derepression of the SOS genes. If LexA were not constitutively expressed, there might be a delay in the availability of LexA protein to be cleaved, which could delay the DNA repair process.
Evaluate the consequences of delayed response: Delay in the activation of SOS genes could result in accumulation of DNA errors or damage, which could be detrimental to the cell. Thus, constitutive expression of lexA ensures a swift and efficient response to DNA damage.
Reflect on evolutionary advantage: The constitutive expression of lexA likely provides an evolutionary advantage by allowing cells to maintain genomic integrity and survive under conditions that cause DNA damage. This rapid response mechanism is crucial for survival in environments with fluctuating levels of DNA-damaging agents.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
3m
Was this helpful?

Key Concepts

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

SOS Response

The SOS response is a global response to DNA damage in bacteria, particularly in Escherichia coli. It involves the activation of a set of genes, known as the SOS regulon, that are responsible for DNA repair and cell cycle regulation. This response is crucial for maintaining genomic integrity and allows the cell to survive under stress conditions that could lead to mutations or cell death.
Recommended video:
Guided course
03:06
Inflammatory Response

lexA Gene

The lexA gene encodes a repressor protein that inhibits the expression of SOS response genes under normal conditions. When DNA damage occurs, the repressor is cleaved, leading to the activation of the SOS regulon. The constitutive expression of lexA ensures that the cell is always prepared to respond to DNA damage, allowing for a rapid activation of repair mechanisms when needed.
Recommended video:
Guided course
05:02
Genes & Alleles

Constitutive Expression

Constitutive expression refers to the continuous production of a gene product, regardless of environmental conditions. In the case of the lexA gene, its constitutive expression allows for a baseline level of regulation over the SOS response. This ensures that the cell can quickly respond to DNA damage, as the repressor is always present to modulate the expression of repair genes when necessary.
Recommended video:
Guided course
06:40
Introduction to Regulation of Gene Expression
Related Practice
Textbook Question
Evaluate these statements about regulation of the lac operon. Select True or False for each statement.T/FThe lac operon is transcribed at the highest rate when extracellular glucose and lactose are abundant.T/FThe repressor protein is bound to DNA of the operator when lactose is present.T/FA mutation in the operator is likely to prevent transcription of the lac operon under any condition.T/FA mutation that alters the catabolite activator protein is predicted to alter the regulation of many different operons.
1076
views
Textbook Question

Predict what would happen to regulation of the lac operon if the lacI gene were moved 50,000 nucleotides upstream of its normal location.

781
views
Textbook Question
Predict what would happen to regulation of the lac operon if the lacI gene were moved 50,000 nucleotides upstream of its normal location.
800
views
Textbook Question
IPTG is a molecule with a structure much like 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 ββ-galactosidase. Predict what would occur to lac operon regulation if IPTG were added to E. coli growth medium containing no glucose or lactose.
1474
views
Textbook Question
In a mutant that lacks adenylyl cyclase, the enzyme that synthesizes cAMP, predict which of the following conditions of extracellular lactose and glucose would cause regulation of the lac operon to differ from that of wild-type cells.a. no lactose, no glucoseb. no lactose, abundant glucosec. abundant lactose, no glucosed. abundant lactose, abundant glucose
822
views
Textbook Question
X-gal is a colorless, lactose-like molecule that can be split into two fragments by ββ-galactosidase. One of these product molecules creates a blue color. The photograph here shows E. coli colonies growing in a medium that contains X-gal. Find three colonies whose cells have functioning copies of ββ-galactosidase. Find three colonies whose cells might have mutations in the lacZ or the lacY genes. Suppose you analyze the protein-coding sequence of the lacZ and lacY genes of cells from the three mutant colonies and find that these sequences are wild type (normal). What other region of the lac operon might be altered to account for the mutant phenotype of these colonies?
1298
views