Lac Operon Regulation – AP Biology

Inducible Operon System

Promoter (P): Binding site for RNA Polymerase.

Operator (O): On/Off switch. Binding site for the Repressor.

Structural Genes: Code for lactase enzymes (\(lacZ, lacY, lacA\)).

The Players

Repressor: Blocks RNA Pol when active (no lactose).

Lactose (Inducer): Binds to the repressor, changing its shape so it falls off.

RNA Polymerase: Transcribes genes when the operator is physically clear.

Tags

gene expressionoperontranscriptionE. coli

Transcription:OFF

Repressor State:Active (Bound)

Lactose Count:0

Environment Control

Negative Control Mechanism

The Lac Operon is an Inducible System. By default, it is OFF because the repressor sits on the operator.

When Lactose is present, it acts as an inducer, releasing the repressor and turning the genes ON.

Note: Once the enzymes are synthesized, they digest the lactose. As lactose levels fall, the repressor rebinds, turning the system OFF automatically.