Bacteria require both lactose and glucose to be present to synthesise protein linked to a lac operon.

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The statement to evaluate is: 'Bacteria require both lactose and glucose to be present to synthesise protein linked to a lac operon.'

Option 1: True. This is not correct. In lac operon regulation, lactose (via allolactose) acts as the inducer that binds the repressor and enables transcription. Glucose is not required for induction; in fact, the presence of glucose typically lowers cAMP levels, which reduces CAP-cAMP activation and can decrease transcription levels. Therefore, lactose alone can induce lac operon expression, especially when glucose is absent or scarce. Saying both must be present misrepresents the regulatory mechanism.

Option 2: False. This is the correct characterization. The lac operon can be induced primarily by lactose even without glucose, although glucose presence modulates the level of expression through catabolite repression (low glucose means high cAMP, active CAP, and stronger transcription). The essential requirement for induction is the presence of lactose (or allolactose) to inactivate the repressor; glucose is not required for transcription to occur.

BPS3021 S1 2025 CYL | Controlling Protein Expression

Bacteria require both lactose and glucose to be present to synthesise protein linked to a lac operon.

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