Read Diauxic Growth and Catabolite Repression
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Diauxic Growth and Catabolite Repression is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Core idea
When glucose and lactose are both present, E. coli preferentially uses glucose. Low cAMP keeps cAMP–CRP activation weak, while inducer availability also governs lac repressor release. Once glucose falls, lac-operon expression and lactose-metabolising enzymes rise, producing a lag before the second growth phase. This is a regulatory adaptation, not a pause caused by osmotic shock.
cAMP-CRP and lac operon
While glucose is abundant, low cAMP and catabolite repression limit lac operon expression. The lag reflects synthesis of lactose-metabolising machinery after glucose depletion.
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- ✓When glucose and lactose are both present, E.
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