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Chapter 16: Problem 56

What happens when tryptophan is present? a. The repressor binds to the operator, and RNA synthesis is blocked. b. RNA polymerase binds to the operator, and RNA synthesis is blocked. c. Tryptophan binds to the repressor, and RNA synthesis proceeds. d. Tryptophan binds to RNA polymerase, and RNA synthesis proceeds.

Short Answer

Expert verified
a. The repressor binds to the operator, and RNA synthesis is blocked.

Step by step solution

01

Understanding the Tryptophan Operon Concept

The tryptophan operon is a group of genes used by bacteria, like E. coli, to regulate the production of tryptophan. When tryptophan is abundant, it acts to turn off the operon.
02

Role of Tryptophan in Regulation

When tryptophan is present, it binds to the repressor protein. This complex then binds to the operator region of the operon.
03

Effect on RNA Synthesis

When the repressor-tryptophan complex binds to the operator, it prevents RNA polymerase from transcribing the genes required for tryptophan synthesis.
04

Recap of Key Points

When tryptophan is present: (1) Tryptophan binds to the repressor, (2) The repressor binds to the operator, and (3) RNA synthesis is blocked.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Gene Regulation
Gene regulation is the process by which cells control the expression and timing of genes. It ensures that genes are turned on or off as needed, which is crucial for the cell's ability to respond to changes and maintain homeostasis. In bacteria like E. coli, the tryptophan operon is a classic example of this regulatory mechanism.
When the environment changes, such as when tryptophan levels increase, genes involved in tryptophan synthesis can be repressed to save energy.
Repressor Protein
A repressor protein is a key player in negative gene regulation. It helps block the transcription of specific genes by binding to an operator region on the DNA. In the case of the tryptophan operon, the repressor protein is inactive by default. However, when tryptophan is present, it binds to the repressor.
This tryptophan-repressor complex can then attach to the operator, effectively blocking RNA polymerase from accessing the genes needed to synthesize more tryptophan.
RNA Synthesis
RNA synthesis, or transcription, is the process where RNA polymerase reads the DNA template to create an RNA strand. This RNA strand can then be translated into proteins. In regulated operons like the tryptophan operon, RNA synthesis can be blocked to prevent unnecessary protein production.
When the tryptophan-repressor complex binds to the operator, it prevents RNA polymerase from initiating transcription of the tryptophan synthesis genes. Consequently, no RNA is produced for those genes, and tryptophan production is halted.

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Most popular questions from this chapter

The enzyme ployadenylate polymerase catalyzes the addition of adenosine monophosphate to the 3鈥� ends of mRNAs to form a poly-A tail. If the enzyme were blocked so that it could not function, the result would be: a. increased mRNA stability in eukaryotes, and decreased mRNA stability in prokaryotes b. decreased mRNA stability in eukaryotes, and no effect in prokaryotes c. no effect in eukaryotes, and increased mRNA stability in prokaryotes d. no effect in eukaryotes, and decreased mRNA stability in prokaryotes

What would be the outcome of a mutation that prevented DNA binding proteins from being produced? a. decreased transcription because transcription factors would not bind to transcription binding sites b. decreased transcription because enhancers would not be able to bind to transcription factors c. increased transcription because repressors would not be able to bind to promoter regions d. increased transcription because RNA polymerase would be able to increase binding to promoter regions

Post-translational modifications of proteins can affect which of the following? a. mRNA splicing b. 5鈥檆apping c. 3鈥檖olyadenylation d. chemical modifications

What would happen if the operator sequence of the trp operon contained a mutation that prevented the repressor protein from binding to the operator? a. In the absence of tryptophan, the genes trpA-E will not be transcribed. b. In the absence of tryptophan, only genes trpE and trpD will be transcribed. c. In the presence of tryptophan, the genes trpA-E will be transcribed. d. In the presence of tryptophan, the trpE gene will not be transcribed.

Flowering Locus C (FLC) is a gene that is responsible for flowering in certain plants. FLC is expressed in new seedlings, which prevents flowering. Upon exposure to cold temperatures, FLC expression decreases and the plant flowers. FLC is regulated through epigenetic modifications. What type of epigenetic modifications are present in new seedlings and after cold exposure? a. In new seedlings, histone acetylations are present; upon cold exposure, methylation occurs. b. In new seedlings, histone deacetylations are present; upon cold exposure, methylation occurs. c. In new seedlings, histone methylations are present; upon cold exposure, acetylation occurs. d. In new seedlings, histone methylations are present; upon cold exposure, deacetylation occurs
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