Skip to main content
Pearson+ LogoPearson+ Logo
Ch. 16 - Regulation of Gene Expression in Bacteria
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of Genetics ISBN: 9780135564776Not the one you use?Change textbook
All textbooksKlug 12th EditionCh. 16 - Regulation of Gene Expression in BacteriaProblem 8
Chapter 16, Problem 8

Describe the experimental rationale that allowed the lac repressor to be isolated.

Verified step by step guidance
1
Understand the biological context: The lac repressor is a protein that regulates the lac operon in bacteria by binding to the operator region and preventing transcription in the absence of lactose.
Recognize the experimental goal: Scientists aimed to isolate the lac repressor protein to study its properties and understand how it controls gene expression.
Identify the key experimental approach: Researchers used a DNA fragment containing the lac operator sequence as a 'bait' to specifically bind the lac repressor protein from a mixture of cellular proteins.
Explain the binding assay: By incubating bacterial extracts with the operator DNA and then separating bound from unbound proteins, the lac repressor could be selectively isolated due to its specific affinity for the operator sequence.
Highlight the use of mutants and inducers: Mutant strains lacking the repressor or using inducers like IPTG helped confirm the identity of the isolated protein by showing changes in binding behavior, thus validating the experimental rationale.

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.

Lac Operon Regulation

The lac operon is a set of genes involved in lactose metabolism in E. coli, regulated by the lac repressor protein. Understanding how the repressor binds to the operator region to inhibit transcription is fundamental to grasping the experimental rationale for its isolation.
Recommended video:
Guided course
06:55
Lac Operon Regulation

Protein-DNA Binding Specificity

The lac repressor specifically binds to the operator DNA sequence, preventing RNA polymerase from transcribing the operon. This specific interaction was exploited experimentally to isolate the repressor by using DNA affinity techniques.
Recommended video:
Guided course
05:05
Proteins

Affinity Chromatography and Experimental Design

The isolation of the lac repressor involved using operator DNA attached to a solid matrix to capture the repressor protein from cell extracts. This approach, based on affinity chromatography principles, allowed selective purification of the repressor by exploiting its DNA-binding property.
Recommended video:
Guided course
05:48
Transformation
Related Practice
Textbook Question

For the lac genotypes shown in the following table, predict whether the structural genes (Z) are constitutive, permanently repressed, or inducible in the presence of lactose. Genotype Constitutive Repressed Inducible I⁺O⁺Z⁺ x I⁻O⁺Z⁺ I⁻OᶜZ⁺ I⁻OᶜZ⁺/F'O⁺ I⁺OᶜZ⁺/F'O⁺ IˢO⁺Z⁺ IˢO⁺Z⁺/F'I⁺

1491
views
Textbook Question

For the genotypes and conditions (lactose present or absent) shown in the following table, predict whether functional enzymes, nonfunctional enzymes, or no enzymes are made.

<IMAGE>

1032
views
Textbook Question

The locations of numerous lacI⁻ and lacIˢ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI⁻ mutations were found to occur in the 5′-upstream region of the gene, while lacIˢ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?

666
views
Textbook Question

What properties demonstrate that the lac repressor is a protein? Describe the evidence that it indeed serves as a repressor within the operon system.

819
views
Textbook Question

Predict the effect on the inducibility of the lac operon of a mutation that disrupts the function of:

(a) The CRP gene, which encodes the CAP protein

(b) The CAP-binding site within the promoter.

951
views
Textbook Question

Erythritol, a natural sugar abundant in fruits and fermenting foods, is about 65 percent as sweet as table sugar and has about 95 percent fewer calories. It is 'tooth friendly' and generally devoid of negative side effects as a human consumable product. Pathogenic Brucella strains that catabolize erythritol contain four closely spaced genes, all involved in erythritol metabolism. One of the four genes (eryD) encodes a product that represses the expression of the other three genes. Erythritol catabolism is stimulated by erythritol. Present a simple regulatory model to account for the regulation of erythritol catabolism in Brucella. Does this system appear to be under inducible or repressible control?

554
views