Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

12. Gene Regulation in Prokaryotes

Lac Operon

Genetics

12. Gene Regulation in Prokaryotes

Lac Operon

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0:38 minutes

Problem 1b

Textbook Question

What evidence established that lactose serves as the inducer of a gene whose product is related to lactose metabolism?

Verified step by step guidance

Understand the concept of an inducer: An inducer is a molecule that initiates or enhances the expression of specific genes. In the case of lactose metabolism in bacteria, lactose acts as the inducer by interacting with the regulatory proteins controlling the expression of genes involved in lactose utilization.

Review the experimental setup: Researchers studied the lac operon in *E. coli*, a model system for understanding gene regulation. They observed that the presence of lactose in the growth medium led to the production of enzymes like β-galactosidase, which are necessary for lactose metabolism.

Analyze the key experiments: One pivotal experiment involved growing *E. coli* in media with and without lactose. In the presence of lactose, the production of β-galactosidase and other enzymes increased significantly, while in its absence, these enzymes were produced at very low levels or not at all.

Consider the role of mutants: Mutants that could not metabolize lactose (e.g., lacZ mutants) were studied. These mutants lacked functional β-galactosidase, confirming that the enzyme was essential for lactose metabolism. Additionally, mutants with defects in the lacI gene (repressor) showed constitutive expression of the lac operon, indicating that lactose interacts with the repressor to induce gene expression.

Conclude based on the evidence: The experiments demonstrated that lactose or its derivative (allolactose) binds to the lac repressor, causing it to release from the operator region of the lac operon. This allows RNA polymerase to transcribe the genes required for lactose metabolism, establishing lactose as the inducer.

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Key Concepts

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

Inducer in Gene Regulation

An inducer is a molecule that initiates gene expression by binding to a repressor protein, thereby allowing transcription to occur. In the context of lactose metabolism in bacteria, lactose acts as an inducer for the lac operon, which encodes enzymes necessary for the breakdown of lactose. This concept is crucial for understanding how bacteria adapt to available nutrients.

Lac Operon Model

The lac operon is a well-studied model of gene regulation in E. coli, consisting of genes that encode proteins for lactose metabolism. It includes a promoter, operator, and structural genes (lacZ, lacY, and lacA). The operon is regulated by the presence or absence of lactose, illustrating how bacteria can efficiently manage their resources based on environmental conditions.

Experimental Evidence in Genetics

Experimental evidence in genetics often involves techniques such as gene knockout, reporter assays, and biochemical assays to demonstrate the function of specific genes or molecules. In the case of lactose as an inducer, experiments showed that the presence of lactose led to increased expression of lac operon genes, providing direct evidence of its role in regulating gene expression related to lactose metabolism.

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Related Practice

Textbook Question

Bacterial genomes frequently contain groups of genes organized into operons. What is the biological advantage of operons to bacteria? Identify the regulatory components you would expect to find in an operon. How are the expressed genes of an operon usually arranged?

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Textbook Question

In this chapter, we focused on the regulation of gene expression in bacteria. Along the way, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions?How do we know that bacteria regulate the expression of certain genes in response to the environment?

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Textbook Question

How do we know that the lac repressor is a protein?

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Textbook Question

What led researchers to conclude that a repressor molecule regulates the lac operon?

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Textbook Question

Transcriptional regulation of operon gene expression involves the interaction of molecules with one another and of regulatory molecules with segments of DNA. In this context, define and give an example of each of the following:

Negative regulation

Allostery

Positive regulation