Lac operon in e coli is switched on when???

1 Answer
alper_ss
May 9, 2018

When glucose is absent and lactose is present.

Explanation:

lac respressor is released from the operator because allolactose is present.
cAMP levels are high because glucose is absent, so Catabolite Activator Protein is active and bound to the operon. CAP helps RNA Polymerase bind to the promoter, permitting high levels of transcription.
Also, there is a low-level transcription when both glucose and lactose is present. Don't know if that counts as "switched on" though.

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