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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2:51 minutes

Problem 25d

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 start (AUG) codon of the trpL polypeptide is deleted.

Verified step by step guidance

Understand the role of the trpL region in attenuation control: The trpL region is part of the leader sequence of the trp operon and contains a short polypeptide coding sequence. This region plays a critical role in regulating transcription through attenuation, which depends on the coupling of transcription and translation in prokaryotes.

Recognize the importance of the start codon (AUG): The start codon is essential for initiating translation of the trpL polypeptide. Without it, the ribosome cannot begin translating the leader peptide, which disrupts the formation of the leader polypeptide.

Analyze the impact on ribosome stalling: In normal conditions, the ribosome stalls at the trp codons in the leader sequence when tryptophan levels are low, allowing the formation of an antiterminator structure in the mRNA. If the start codon is deleted, translation of the leader peptide cannot occur, preventing ribosome stalling and disrupting attenuation control.

Consider the effect on transcription termination: Without ribosome stalling, the terminator structure (a stem-loop followed by a poly-U sequence) may form regardless of tryptophan levels. This could lead to premature termination of transcription of the trp operon genes, reducing their expression even when tryptophan is scarce.

Summarize the likely outcome: The deletion of the start codon in the trpL region would likely impair attenuation control, leading to a loss of proper regulation of the trp operon. This could result in reduced transcription of the operon genes under conditions where tryptophan is needed.

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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 continues or is terminated prematurely. This process is sensitive to the levels of tryptophan, allowing the cell to adjust gene expression based on nutrient availability.

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, allowing the cell to efficiently manage resources and respond to changes in tryptophan levels, ensuring that the synthesis of tryptophan occurs only when needed.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can affect gene function. In the context of the trpL region, a deletion of the start codon (AUG) would prevent the synthesis of the trpL polypeptide, disrupting the formation of the necessary RNA structures for proper attenuation control, potentially leading to continuous transcription of the trp operon regardless of tryptophan levels.

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Related Practice

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.

Two nucleotides are inserted immediately following the polypeptide start codon.

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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.

Ten nucleotides are inserted between regions 2 and 3 of trpL.

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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.

Twenty nucleotides are inserted into the trpL region immediately after the polypeptide stop codon.

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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.

Two nucleotides are inserted into the trpL region immediately after the polypeptide stop codon.

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Textbook Question

The function of tRNA synthetases is to attach amino acids to tRNAs. Suppose the tRNA synthetase responsible for attaching tryptophan to tRNA is mutated in a bacterial strain, with the result that the tRNA synthetase functions at about 15% of the efficiency of the wild-type tRNA synthetase. Would formation of the 3–4 stem-loop structure in mRNA be more frequent or less frequent in the mutant strain than in the wild-type strain? Why?

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Textbook Question

How would this mutation affect attenuation of the tryptophan operon? Explain your answer.

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Multiple Choice

Which of the following evidence best supports the claim that tryptophan functions as a corepressor in the trp operon?

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Multiple Choice

Tryptophan regulates the trp operon by doing what?

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