Multiple Choice
How does the cell recognize that lactose needs to be metabolized in the lac operon system?
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16. Regulation of Expression
The Lac Operon
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Which of the following conditions is most likely to result in transcription of the lac operon?
A
Low levels of lactose and high levels of glucose
B
High levels of lactose and high levels of glucose
C
High levels of lactose and low levels of glucose
D
Low levels of lactose and low levels of glucose
Verified step by step guidance1
Understand the role of the lac operon: It is a set of genes involved in the metabolism of lactose in bacteria, primarily E. coli. The operon is regulated by the presence or absence of lactose and glucose.
Identify the key components: The lac operon includes the lacZ, lacY, and lacA genes, which are controlled by a promoter, an operator, and a repressor protein. The presence of lactose inactivates the repressor, allowing transcription.
Consider the effect of glucose: High levels of glucose inhibit the production of cyclic AMP (cAMP), which is necessary for the activation of the catabolite activator protein (CAP). CAP, when bound to cAMP, enhances the transcription of the lac operon.
Analyze the given conditions: For the lac operon to be transcribed, lactose must be present to inactivate the repressor, and glucose must be low to allow cAMP levels to rise, enabling CAP to bind to the promoter region.
Conclude with the correct condition: High levels of lactose and low levels of glucose create an environment where the repressor is inactive and CAP is active, leading to the transcription of the lac operon.
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