Lac Operon Induction and Catabolite Repression
The lac operon demonstrates how E. coli regulates gene expression in response to two environmental signals — lactose availability and glucose scarcity. Understanding both induction (the role of allolactose and the lac repressor) and catabolite repression (cAMP-CAP) is crucial for AP Biology Unit 6 (Gene Expression) and is a classic AP exam free-response topic. These cards clarify how both control systems interact.
Interactive Deck
5 CardsWhat happens to cAMP levels when glucose is present?
Name the three structural genes of the lac operon and their products.
Master this topic effortlessly.
Study G helps you master any topic effortlessly using proven learning algorithms and smart review timing
Download Study GFrequently Asked Questions
What is catabolite repression in the lac operon?
Catabolite repression is reduced lac operon transcription when glucose is present. High glucose lowers cAMP, preventing CAP from activating the promoter — even if lactose is available. E. coli preferentially metabolizes glucose before lactose.
What is the difference between the lac repressor and CAP?
The lac repressor is a negative regulator — it blocks transcription when lactose is absent. CAP (catabolite activator protein) is a positive regulator — it enhances transcription when glucose is absent and cAMP is high.
How do I remember what controls each part of the lac operon?
Lactose controls the repressor (allolactose removes negative repression). Glucose controls CAP via cAMP — no glucose = high cAMP = CAP active. Maximum transcription requires lactose present AND glucose absent simultaneously.