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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0:26 minutes

Problem 1c

Textbook Question

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

Verified step by step guidance

Understand the lac operon: The lac operon is a set of genes in bacteria responsible for metabolizing lactose. It includes structural genes (lacZ, lacY, lacA), a promoter, an operator, and a regulatory gene (lacI). The lacI gene produces a repressor protein that binds to the operator to inhibit transcription.

Review experimental evidence: Researchers observed that in the absence of lactose, the lac operon is not expressed, suggesting a regulatory mechanism. When lactose is present, the operon becomes active, indicating that lactose interacts with the regulatory system.

Examine the role of the repressor: Mutations in the lacI gene led to constitutive expression of the lac operon, meaning it was active regardless of lactose presence. This suggested that the lacI gene product (the repressor) is necessary to inhibit operon expression in the absence of lactose.

Analyze the effect of lactose: Researchers found that lactose (or its derivative, allolactose) binds to the repressor molecule, causing a conformational change that prevents the repressor from binding to the operator. This allows RNA polymerase to transcribe the operon genes.

Conclude the regulatory mechanism: Based on these observations, researchers concluded that the lac operon is regulated by a repressor molecule produced by the lacI gene. The repressor binds to the operator to block transcription, and lactose acts as an inducer by inactivating the repressor.

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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 bacteria, specifically E. coli, that are involved in the metabolism of lactose. It consists of structural genes that encode proteins necessary for lactose uptake and breakdown, and it is regulated by a promoter and an operator. Understanding the lac operon is crucial for grasping how bacteria adapt to different energy sources and how gene expression is controlled in response to environmental changes.

Repressor Molecule

A repressor molecule is a type of protein that binds to specific DNA sequences, inhibiting the transcription of certain genes. In the context of the lac operon, the lac repressor binds to the operator region, preventing RNA polymerase from transcribing the downstream genes when lactose is absent. This mechanism is a key example of negative regulation in gene expression, demonstrating how cells conserve resources by only expressing genes when necessary.

Gene Regulation Mechanisms

Gene regulation mechanisms refer to the various processes that control the timing and amount of gene expression in an organism. In bacteria, these mechanisms include operons, repressors, and activators, which respond to environmental signals. Understanding these mechanisms is essential for explaining how researchers deduced the role of the repressor in the lac operon, as they illustrate the dynamic interactions between genes and their regulatory elements.

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Related Practice

Textbook Question

What are the advantages and disadvantages of using GFP versus lacZ as a reporter gene in mice, C. elegans, and Drosophila?

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

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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