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Chapter 16: Problem 17

Both attenuation of the \(t r p\) operon in \(E\). coli and riboswitches in B. subtilis rely on changes in the secondary structure of the leader regions of mRNA to regulate gene expression. Compare and contrast the specific mechanisms in these two types of regulation.

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Question: Compare and contrast the specific mechanisms of gene regulation in the attenuation of the trp operon in E. coli and riboswitches in B. subtilis. Answer: Both trp operon attenuation in E. coli and riboswitches in B. subtilis involve changes in the secondary structure of the leader regions of mRNA in response to regulatory molecules. In trp operon attenuation, tryptophan and the repressor protein act as regulatory molecules, while in riboswitches, specific metabolites or ions directly bind the mRNA. Attenuation of the trp operon functions primarily to turn off gene expression when tryptophan levels are high, while riboswitches can either inhibit or stimulate gene expression depending on the specific riboswitch and associated metabolite.

Step by step solution

01

The trp operon in E. coli regulates the synthesis of the amino acid tryptophan. When tryptophan levels are high, the operon is turned off, whereas when tryptophan levels are low, the operon is turned on. Attenuation of the trp operon involves changes in the secondary structure of the trp leader mRNA, which affects the transcription of the structural genes. #Step 2: Understand riboswitches in B. subtilis#

Riboswitches are RNA sequences found in the leader regions of certain mRNAs, which regulate gene expression through conformational changes in response to binding of a specific metabolite or ion. B. subtilis is a Gram-positive bacterium, and riboswitches are involved in regulating various genes, including those for amino acid synthesis. In B. subtilis, riboswitches can either inhibit or stimulate gene expression depending on the specific riboswitch and the associated metabolite. #Step 3: Compare the mechanisms of action in attenuation and riboswitches#
02

Both attenuation and riboswitches rely on the changes in the secondary structure of the leader regions of mRNA. In the case of the trp operon attenuation, when tryptophan levels are high, a transcription attenuation mechanism takes place. The leader mRNA forms a terminator hairpin loop, which leads to premature termination of transcription. In the case of riboswitches in B. subtilis, binding of a specific metabolite to the riboswitch triggers a conformational change in the mRNA, which either exposes or hides regulatory elements, such as transcription terminators or ribosome binding sites. #Step 4: Contrast the roles of regulatory molecules in attenuation and riboswitches#

In the trp operon attenuation, the regulatory molecule is tryptophan itself, which acts as a co-repressor by binding to the trp repressor protein. Tryptophan does not directly bind to the mRNA. In riboswitches, the regulatory molecule is the specific metabolite or ion, which directly binds to the riboswitch sequence within the mRNA leader region, inducing the conformational change and affecting gene expression. #Step 5: Compare gene regulation effects in attenuation and riboswitches#
03

In the trp operon attenuation, when tryptophan levels are high and the attenuation mechanism is active, transcription of the structural genes is terminated. In the case of riboswitches, binding of the specific metabolite can lead to either inhibition or activation of gene expression, depending on the riboswitch and the associated metabolite. For example, some riboswitches can cause transcription termination or prevent ribosome binding, while others can stimulate gene expression by stabilizing the mRNA and preventing degradation. #Step 6: Conclusion#

In summary, both trp operon attenuation in E. coli and riboswitches in B. subtilis involve the changes in the secondary structure of the leader regions of mRNA in response to regulatory molecules. While attenuation of the trp operon functions primarily to turn off gene expression when tryptophan levels are high, riboswitches can either inhibit or stimulate gene expression, depending on the specific riboswitch and associated metabolite. The regulatory molecules in trp operon attenuation are mainly tryptophan and the repressor protein, while in riboswitches, the regulatory molecules are specific metabolites or ions that directly bind the mRNA.

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Most popular questions from this chapter

Assume that the structural genes of the lac operon have been fused, through recombinant DNA techniques, to the regulatory apparatus of the ara operon. If arabinose is provided in a minimal medium to \(E\). coli carrying this gene fusion, would you expect \(\beta\) -galactosidase to be produced at induced levels? Explain.

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