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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1:36 minutes

Problem 1d

Textbook Question

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

Verified step by step guidance

Understand the context: The lac repressor is a key regulatory protein in the lac operon system of *E. coli*. It binds to the operator region to inhibit transcription of genes involved in lactose metabolism. To determine that the lac repressor is a protein, experimental evidence is required.

Step 1: Review the biochemical isolation of the lac repressor. Scientists used techniques such as affinity chromatography to isolate the lac repressor from bacterial cells. This method relies on the specific binding of the repressor to DNA sequences containing the operator region.

Step 2: Analyze the molecular composition of the isolated lac repressor. Once isolated, the lac repressor was subjected to protein analysis techniques, such as gel electrophoresis and amino acid sequencing, which confirmed that it is composed of amino acids, the building blocks of proteins.

Step 3: Examine the functional properties of the lac repressor. Proteins are known to have specific three-dimensional structures that allow them to perform their functions. The lac repressor was shown to bind specifically to the operator DNA sequence, a characteristic behavior of proteins with DNA-binding domains.

Step 4: Consider the effects of mutations in the lacI gene. The lacI gene encodes the lac repressor. Mutations in lacI that disrupt the production of the repressor or alter its structure result in changes to the regulation of the lac operon, further supporting that the lac repressor is a protein encoded by this gene.

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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 well-studied model of gene regulation in bacteria, particularly in Escherichia coli. It consists of genes responsible for the metabolism of lactose and is controlled by the lac repressor protein. Understanding the lac operon is crucial for grasping how gene expression is regulated in response to environmental changes, such as the presence or absence of lactose.

Protein Function and Identification

Proteins are essential biomolecules that perform a variety of functions in living organisms, including acting as enzymes, structural components, and regulators of gene expression. The identification of the lac repressor as a protein was established through various biochemical techniques, such as gel electrophoresis and affinity chromatography, which separate and characterize proteins based on their size and binding properties.

Experimental Evidence

Experimental evidence is critical in molecular biology for validating hypotheses about biological processes. In the case of the lac repressor, experiments such as the use of mutations, protein purification, and functional assays demonstrated that the repressor binds to the operator region of the lac operon, inhibiting transcription when lactose is absent, thereby confirming its role as a protein.

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Related Practice

Multiple Choice

Glucose concentration can regulate the lac operon?

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

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

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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

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