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

Tryptophan Operon and Attenuation

Genetics

12. Gene Regulation in Prokaryotes

Tryptophan Operon and Attenuation

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2:25 minutes

Problem 25c

Textbook Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.
The entire trpL region is deleted.

Verified step by step guidance

Understand the role of the trpL region: The trpL region is part of the leader sequence in the trp operon. It contains sequences that form stem-loop structures in the mRNA, which are critical for attenuation control. Attenuation is a regulatory mechanism that halts transcription of the trp operon when tryptophan levels are sufficient.

Recognize the impact of deleting the trpL region: Without the trpL region, the leader sequence cannot form the necessary stem-loop structures. These structures are essential for sensing tryptophan levels and regulating transcription termination.

Consider the consequences for attenuation: In the absence of the trpL region, attenuation control is likely disrupted. This means the operon may no longer respond properly to tryptophan levels, leading to unregulated transcription of the trp operon genes regardless of tryptophan availability.

Explain the reasoning: The deletion removes the sequences required for the formation of the terminator stem-loop and the anti-terminator stem-loop. These structures are key to the attenuation mechanism, which relies on ribosome stalling and the formation of specific secondary structures in the mRNA.

Conclude the likely effect: The deletion of the trpL region would likely result in constitutive transcription of the trp operon genes, as attenuation control is entirely lost. This could lead to overproduction of enzymes involved in tryptophan synthesis, even when tryptophan is abundant.

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Key Concepts

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

Attenuation Control

Attenuation control is a regulatory mechanism in prokaryotic gene expression, particularly in the trp operon, where the formation of specific RNA structures in the leader region (trpL) determines whether transcription will continue or terminate. This process relies on the availability of tryptophan and the ribosome's movement along the mRNA, influencing the formation of either a transcription-terminating or a transcription-allowing structure.

trp Operon

The trp operon is a cluster of genes in bacteria that encode enzymes necessary for the biosynthesis of the amino acid tryptophan. It is regulated by both repression and attenuation mechanisms, allowing the cell to efficiently manage tryptophan levels. The operon includes a leader sequence (trpL) that plays a crucial role in the attenuation process.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can affect gene function and regulation. In the context of the trp operon, a deletion of the trpL region would eliminate the leader sequence responsible for attenuation control. This would likely result in continuous transcription of the operon, leading to overproduction of tryptophan, as the regulatory feedback mechanism would be disrupted.

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Related Practice

Textbook Question

Attenuation of the trp operon was viewed as a relatively inefficient way to achieve genetic regulation when it was first discovered in the 1970s. Since then, however, attenuation has been found to be a relatively common regulatory strategy. Assuming that attenuation is a relatively inefficient way to achieve genetic regulation, what might explain its widespread occurrence?

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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

A repressible operon system, like the trp operon, contains three genes, G, Z, and W. Operon genes are synthesized when the end product of the operon synthesis pathway is absent, but there is no synthesis when the end product is present. One of these genes is an operator, one is a regulatory protein, and the other is a structural enzyme involved in synthesis of the end product. In the table below, '+' indicates that the enzyme is synthesized by the operon and '−' means that no enzyme synthesis occurs. Use this information to determine which gene corresponds to each operon function.

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Textbook Question

The following figure depicts numerous critical regions of the leader sequence of mRNA that play important roles during the process of attenuation in the trp operon. A closer view of the leader sequence, which begins at about position 30 downstream from the 5' end, is shown below, running along both columns. Within this molecule are the sequences that cause the formation of the alternative hairpins. It also contains the successive triplets that encode tryptophan, where stalling during translation occurs.

Take a large piece of paper (such as manila wrapping paper) and, along with several other students from your genetics class, work through the base sequence to identify the trp codons and the parts of the molecule representing the base-pairing regions that form the terminator and antiterminator hairpins shown in the following figure.

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Textbook Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

Region 4 is deleted.

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Textbook Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

Region 3 is deleted.

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Textbook Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

The eight uracil nucleotides immediately following region 4 are deleted.

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Textbook Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

The entire polypeptide coding sequence of trpL is deleted.

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