Textbook Question
In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the lacI gene affecting the DNA-binding site of the protein
Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172
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Table of contents
- Ch. 1 - The Molecular Basis of Heredity, Variation, and Evolution64
- Ch. 2 - Transmission Genetics144
- Ch. 3 - Cell Division and Chromosome Heredity81
- Ch. 4 - Gene Interaction87
- Ch. 5 - Genetic Linkage and Mapping in Eukaryotes103
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages73
- Ch. 7 - DNA Structure and Replication71
- Ch. 8 - Molecular Biology of Transcription and RNA Processing79
- Ch. 9 - The Molecular Biology of Translation110
- Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization100
- Ch. 11 - Gene Mutation, DNA Repair, and Homologous Recombination86
- Ch. 12 - Regulation of Gene Expression in Bacteria and Bacteriophage90
- Ch. 13 - Regulation of Gene Expression in Eukaryotes38
- Ch. 14 - Analysis of Gene Function via Forward Genetics and Reverse Genetics72
- Ch. 15 - Recombinant DNA Technology and Its Applications69
- Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective49
- Ch. 17 - Organelle Inheritance and the Evolution of Organelle Genomes27
- Ch. 18 - Developmental Genetics43
- Ch. 19 - Genetic Analysis of Quantitative Traits66
- Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels105
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
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Sanders 3rd EditionCh. 12 - Regulation of Gene Expression in Bacteria and BacteriophageProblem 16c
Sanders 3rd EditionCh. 12 - Regulation of Gene Expression in Bacteria and BacteriophageProblem 16cChapter 12, Problem 16c
In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the lacI gene affecting the allosteric site of the protein
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Understand the role of the lacI gene: The lacI gene encodes the lac repressor protein, which binds to the operator region of the lac operon to inhibit transcription. The allosteric site of the lac repressor is where the inducer (allolactose) binds, causing a conformational change that prevents the repressor from binding to the operator.
Analyze the mutation: A mutation in the allosteric site of the lacI gene would likely affect the ability of the repressor protein to bind the inducer (allolactose). This could result in the repressor being unable to undergo the conformational change necessary to release from the operator.
Predict the effect on transcription: If the repressor cannot bind the inducer, it will remain bound to the operator, continuously blocking RNA polymerase from transcribing the operon genes. This would lead to a lack of transcription, even in the presence of lactose.
Consider alternative scenarios: If the mutation causes the allosteric site to mimic the induced state permanently, the repressor may never bind to the operator, leading to constitutive (continuous) transcription of the operon genes, regardless of lactose presence.
Summarize the outcomes: Depending on the specific nature of the mutation, the lac operon could either be permanently repressed (no transcription) or constitutively active (continuous transcription). The exact effect depends on whether the mutation prevents inducer binding or mimics the induced state.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Lac Operon
The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of structural genes (lacZ, lacY, and lacA) and regulatory elements that control their expression. The operon is typically off when lactose is absent and is activated in its presence, allowing the bacteria to utilize lactose as an energy source.
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Lac Operon Overview
LacI Gene and Repressor Protein
The lacI gene encodes the lac repressor protein, which binds to the operator region of the lac operon to inhibit transcription when lactose is not present. The repressor can undergo conformational changes when bound to allolactose, a lactose metabolite, allowing RNA polymerase to access the promoter and initiate transcription of the operon genes.
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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. In the context of the lac operon, mutations affecting the allosteric site of the lac repressor can disrupt its ability to bind allolactose, potentially leading to continuous repression of the operon, even in the presence of lactose.
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Related Practice
Textbook Question
In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of consensus sequence in the lac promoter
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Textbook Question
In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the repressor binding site on the operator sequence
Textbook Question
Identify which of the following lac operon haploid genotypes transcribe operon genes inducibly and which transcribe genes constitutively. Indicate whether the strain is lac⁺ (able to grow on lactose-only medium) or lac⁻ (cannot grow on lactose medium).
I⁺ P⁺ O⁺ Z⁺ Y⁻
Textbook Question
Attenuation of trp operon transcription is controlled by the formation of stem-loop structures in mRNA. The attenuation function can be disrupted by mutations that alter the sequence of repeat DNA regions 1 to 4 and prevent the formation of mRNA stem loops. Describe the likely effects on attenuation of each of the following mutations under the conditions specified.
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Textbook Question
In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the CAP binding site of the lac promoter