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Questions and Answers
What is the primary function of the trp operon?
What is the primary function of the trp operon?
What triggers the binding of the Trp repressor to the trp operator?
What triggers the binding of the Trp repressor to the trp operator?
What happens when tryptophan levels are low in relation to transcription of the trp operon?
What happens when tryptophan levels are low in relation to transcription of the trp operon?
What is the role of attenuation in the regulation of the trp operon?
What is the role of attenuation in the regulation of the trp operon?
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What happens to the proportion of attenuated transcripts as tryptophan concentration increases?
What happens to the proportion of attenuated transcripts as tryptophan concentration increases?
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How many nucleotides of RNA are produced from the trp operon before RNA polymerase encounters the first codon of trpE?
How many nucleotides of RNA are produced from the trp operon before RNA polymerase encounters the first codon of trpE?
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What is the nature of the ligand that controls the activity of the Trp repressor?
What is the nature of the ligand that controls the activity of the Trp repressor?
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What structural feature is present at the 5' end of the trp operon mRNA that contributes to transcription termination?
What structural feature is present at the 5' end of the trp operon mRNA that contributes to transcription termination?
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What role does the hairpin loop play in the trp operon leader sequence?
What role does the hairpin loop play in the trp operon leader sequence?
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How many nucleotides long is the leader RNA typically produced by the trp operon?
How many nucleotides long is the leader RNA typically produced by the trp operon?
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What happens when tryptophan is abundant in the trp operon?
What happens when tryptophan is abundant in the trp operon?
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What is the role of the two tryptophan codons near the stop codon in the trpL gene?
What is the role of the two tryptophan codons near the stop codon in the trpL gene?
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Which pairing prevents the formation of the terminator hairpin in the trp operon?
Which pairing prevents the formation of the terminator hairpin in the trp operon?
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What is the functional consequence of the pairing of regions 3 and 4 in the trp operon leader sequence?
What is the functional consequence of the pairing of regions 3 and 4 in the trp operon leader sequence?
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Which feature of the leader peptide's sequence is critical for its regulatory function in the trp operon?
Which feature of the leader peptide's sequence is critical for its regulatory function in the trp operon?
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What is one of the features of the leader sequence in the trp operon?
What is one of the features of the leader sequence in the trp operon?
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Study Notes
Tryptophan Operon
- The trp operon codes for anabolic enzymes, which are responsible for the biosynthesis of tryptophan, an essential amino acid.
- The trp operon is regulated by two mechanisms: a repressor/operator interaction and attenuation.
Repressor/Operator Interaction
- When tryptophan is present, it binds to an aporepressor protein, forming an active repressor.
- The active repressor binds to the operator, preventing transcription of the trp operon.
- This is an example of negative control, where the presence of the end product (tryptophan) inhibits its own production.
Attenuation
- Attenuation is a second level of regulation that occurs in the trp operon.
- Attenuation involves the formation of alternative hairpin structures within the leader sequence of the trp mRNA.
- These hairpins can either terminate transcription prematurely (attenuation) or allow transcription to proceed.
Leader Sequence
- The leader sequence is a region of the trp mRNA that contains four regions (1, 2, 3, and 4) capable of forming secondary structures through complementary base pairing.
- The leader sequence also encodes a short leader peptide.
Attenuation Mechanism
- The ribosome translating the leader peptide encounters two tryptophan codons in a row.
- If tryptophan is abundant, the ribosome efficiently translates these codons, stalling in region 2. This pairing of regions 1 and 2 is important for the stability of region 2.
- Stalling in region 2 prevents its pairing with region 3. Therefore, region 3 pairs with region 4, forming a terminator hairpin known as the attenuator. Transcription stops prematurely, and the structural genes responsible for tryptophan biosynthesis are not transcribed.
- If tryptophan is scarce, ribosomes stall at the tryptophan codons in the leader peptide. This is because the lack of tryptophan limits the availability of charged tRNA molecules for translation.
- This stalling allows regions 2 and 3 to pair, preventing the formation of the attenuator hairpin. Transcription continues, and the structural genes are transcribed to produce tryptophan.
Charles Yanofsky
- Charles Yanofsky is a renowned geneticist who made significant contributions to understanding the regulation of the trp operon through attenuation.
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Description
Explore the mechanisms regulating the trp operon, including repressor/operator interactions and attenuation. This quiz covers how tryptophan biosynthesis is controlled at the transcriptional level through negative feedback mechanisms. Test your knowledge on the structure and functions of the operon.
