Textbook Question
What evidence established that lactose serves as the inducer of a gene whose product is related to lactose metabolism?
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12. Gene Regulation in Prokaryotes
Lac Operon
1:52 minutesProblem 2e
Textbook Question
Transcriptional regulation of operon gene expression involves the interaction of molecules with one another and of regulatory molecules with segments of DNA. In this context, define and give an example of each of the following:
Promoter
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Understand the concept of a promoter: A promoter is a specific DNA sequence located upstream of a gene that serves as the binding site for RNA polymerase and other transcription factors. It is essential for initiating transcription.
Explain the role of the promoter in transcription: The promoter acts as a regulatory element that determines when and where a gene is expressed. It helps RNA polymerase recognize the start site for transcription.
Provide an example of a promoter: The lac operon in *Escherichia coli* contains a promoter region (lacP) that facilitates the transcription of genes involved in lactose metabolism when lactose is present and glucose is absent.
Discuss the interaction of the promoter with regulatory molecules: In the lac operon, the lac promoter interacts with the lac repressor protein. When lactose is absent, the repressor binds to the operator region, preventing RNA polymerase from accessing the promoter. When lactose is present, the repressor is inactivated, allowing transcription to proceed.
Highlight the importance of promoters in gene regulation: Promoters are critical for controlling gene expression, ensuring that genes are transcribed only under appropriate conditions. Mutations in promoter regions can lead to changes in gene expression levels, which may have significant biological consequences.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Promoter
A promoter is a specific DNA sequence located upstream of a gene that serves as the binding site for RNA polymerase and transcription factors. It is essential for initiating the transcription of the gene into messenger RNA (mRNA). For example, the lac promoter in the lac operon of E. coli is responsible for the transcription of genes involved in lactose metabolism.
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Transcription Factors
Transcription factors are proteins that bind to specific DNA sequences, including promoters, to regulate the transcription of genes. They can act as activators or repressors, influencing the rate of gene expression. For instance, the CAP (catabolite activator protein) enhances the transcription of the lac operon in the presence of cAMP, promoting lactose utilization when glucose levels are low.
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Operon
An operon is a cluster of genes under the control of a single promoter and regulatory elements, allowing coordinated expression of genes with related functions. In prokaryotes, operons enable efficient regulation of metabolic pathways. The lac operon, which includes genes for lactose uptake and metabolism, is a classic example, illustrating how bacteria adapt to environmental changes.
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