Consider a colony of E. coli cells that have a mutation in the lac I gene,...

Consider a colony of E. coli cells that have a mutation in the lac I gene, resulting in a LacR protein that cannot bind to allolactose. Describe the effect that this mutation will have on the lac operon in terms of βgal protein levels when the cells are grown in media containing lactose but no glucose. Explain your reasoning.

Expert Solution

When glucose is present in the medium but not lactose or both glucose and lactose are present in the medium, the lac repressor is bound to operator region so that the Operon is is maintained in a switched off condition. In this condition, repressor is blocking RNA polymerase and therefore transcription of the Lac Operon genes will not take place.

But when there is no glucose in the medium and lactose is present, then lactose molecule act as an inducer and binds to repressor. This leads to the degradation of repressor. This makes operator free of repressor and now RNA polymerase can transcribe the Operon.

But if there is a mutation in the gene encoding for repressor, then the repressor will not be able to bind to lactose. In the absence of this complex formation, there will be no degradation of the repressor and the operator will remain bound to the repressor. In this condition, RNA polymerase will not be able to transcribe the Operon even if glucose is present in the medium. When the overall is not transcribing in this case, then there will be no production of any of the Operon related proteins and therefore beta galactose protein will also not be formed.

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gladiator answered 2 years ago

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