Biology – Gene control | e-Consult

The regulation of the lac operon is an example of negative control because the presence of a molecule (allolactose) actively inhibits the transcription of the operon. In the absence of lactose, the repressor protein binds to the operator, blocking RNA polymerase and preventing gene expression. This is a negative control mechanism – the product (lactose) inhibits the process that produces the product (enzymes for lactose metabolism).

Here's a diagram illustrating the process:

Diagram Description:

• Absence of Lactose: The repressor protein is bound to the operator, blocking RNA polymerase. No transcription occurs.
• Presence of Lactose: Lactose is converted to allolactose. Allolactose binds to the repressor protein, causing a conformational change.
• Repressor Release: The altered repressor detaches from the operator.
• Transcription: RNA polymerase can now bind to the promoter and transcribe the lac operon genes.