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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12. Gene Regulation in Prokaryotes
Tryptophan Operon and Attenuation
1:54 minutesProblem 25e
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.
Verified step by step guidance1
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 peptide-coding region followed by sequences that can form stem-loop structures. These structures are critical for regulating transcription termination based on tryptophan availability.
Analyze the mutation: Two nucleotides are inserted immediately after the polypeptide stop codon in the trpL region. This insertion could potentially disrupt the formation of the stem-loop structures that are essential for attenuation control.
Consider the impact on stem-loop formation: The insertion may shift the reading frame or alter the spacing between sequences that form the stem-loop structures. This could prevent proper formation of the terminator stem-loop, which is responsible for halting transcription when tryptophan levels are high.
Evaluate the effect on transcription: If the terminator stem-loop cannot form correctly, attenuation control may be impaired. This could lead to continued transcription of the trp operon genes even when tryptophan levels are sufficient, resulting in overproduction of tryptophan biosynthetic enzymes.
Summarize the reasoning: The insertion of two nucleotides after the stop codon likely disrupts attenuation control by interfering with the formation of critical stem-loop structures in the trpL region. This would reduce the operon's ability to regulate transcription in response to tryptophan levels.
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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. This process relies on the availability of tryptophan and the ribosome's movement along the mRNA, influencing the formation of a transcription terminator or an anti-terminator structure.
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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.
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Mutations and Their Effects
Mutations are changes in the DNA sequence that can affect gene function and regulation. In the context of the trpL region, inserting nucleotides can alter the RNA structure formed during transcription, potentially disrupting the balance between terminator and anti-terminator formation. This can lead to either increased or decreased transcription of the trp operon, depending on how the mutation affects ribosome movement and RNA folding.
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