The lac operon is an example of which type of operon regulation?

The lac operon is an example of which type of operon regulation?

• A. It is a constitutive operon that metabolizes lactose.
• B. It is an inducible operon that metabolizes lactose.
• C. It is a repressible operon that metabolizes lactose.
• D. It is an operon that metabolizes lactose constitutively.

Answer: (B)

Inducible regulation means the operon is normally off and turned on in response to a specific signal. For the lac operon, the repressor protein binds to the operator and blocks RNA polymerase, so genes needed to metabolize lactose are not expressed when lactose isn’t present. When lactose is around, a portion of it is converted to allolactose, which binds the repressor and changes its shape so it releases the operator. With the repressor no longer blocking, RNA polymerase can transcribe the genes for beta-galactosidase, lactose permease, and transacetylase, enabling the cell to import and break down lactose. This is the hallmark of an inducible operon—expression is activated by a substrate (lactose) rather than being constitutively on or turned off by its end product. (Note: CAP-cAMP can enhance transcription when glucose is low, but the core idea is that lactose presence induces expression.)

Inducible regulation means the operon is normally off and turned on in response to a specific signal. For the lac operon, the repressor protein binds to the operator and blocks RNA polymerase, so genes needed to metabolize lactose are not expressed when lactose isn’t present. When lactose is around, a portion of it is converted to allolactose, which binds the repressor and changes its shape so it releases the operator. With the repressor no longer blocking, RNA polymerase can transcribe the genes for beta-galactosidase, lactose permease, and transacetylase, enabling the cell to import and break down lactose. This is the hallmark of an inducible operon—expression is activated by a substrate (lactose) rather than being constitutively on or turned off by its end product. (Note: CAP-cAMP can enhance transcription when glucose is low, but the core idea is that lactose presence induces expression.)