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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3:07 minutes

Problem 25f

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.

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 sequences that form stem-loop structures, which are critical for attenuation. Attenuation is a regulatory mechanism that controls transcription termination based on tryptophan levels.

Analyze the mutation: The insertion of twenty nucleotides immediately after the polypeptide stop codon in the trpL region could disrupt the formation of the stem-loop structures. These structures are essential for the attenuation mechanism to function properly.

Consider the impact on transcription termination: If the stem-loop structures are altered, the ability of the trp operon to terminate transcription in response to high tryptophan levels may be compromised. This could lead to continued transcription of the operon even when tryptophan is abundant.

Evaluate the effect on gene expression: With attenuation control disrupted, the trp operon genes may be transcribed at higher levels than normal, potentially leading to overproduction of tryptophan biosynthesis enzymes.

Summarize the reasoning: The insertion of twenty nucleotides likely interferes with the attenuation mechanism by altering the secondary structure of the trpL region, resulting in a loss of proper transcriptional regulation of the trp operon.

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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 terminates. This process relies on the coupling of transcription and translation, allowing the cell to respond to the availability of tryptophan by either allowing or halting the synthesis of enzymes involved in its biosynthesis.

trp Operon

The trp operon is a cluster of genes in bacteria that encodes 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 resources based on 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, mutations in the trpL region can alter the formation of RNA secondary structures, impacting the ability of the ribosome to translate the leader peptide and thus influencing the attenuation process. For example, inserting nucleotides may disrupt the normal folding of the RNA, potentially leading to premature termination of transcription or continued expression of the operon.

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