Here are the essential concepts you must grasp in order to answer the question correctly.
Lactose Operon
The lactose operon is a set of genes in bacteria, particularly E. coli, that are responsible for the metabolism of lactose. It consists of structural genes that encode proteins necessary for lactose uptake and breakdown. The operon is regulated by the presence or absence of lactose and glucose, allowing the bacteria to efficiently utilize available energy sources.
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In the Presence of Lactose
Inducer Molecule
In the context of the lactose operon, the inducer molecule is lactose itself, which binds to the repressor protein. This binding causes a conformational change that inactivates the repressor, allowing RNA polymerase to access the promoter region and initiate transcription of the operon. Thus, the presence of lactose is crucial for the operon to be 'on' and actively transcribed.
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Methods of Inducing Mutations
Glucose Repression
Glucose repression is a regulatory mechanism in bacteria where the presence of glucose inhibits the expression of genes involved in the metabolism of other sugars, such as lactose. When glucose levels are high, cyclic AMP (cAMP) levels are low, preventing the activation of the cAMP receptor protein (CRP) that is necessary for the transcription of the lactose operon. Therefore, for the operon to be 'on', glucose must be absent.
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Glucose Levels, cAMP, & the Lac Operon