Specifically describe how the lac operon (enzyme induction) and trp operon (enzyme repression) control gene expression. Use a diagram.

Question 1

Lac Operon: Enzyme Induction

Answer 1

The lac operon helps break down lactose.

• When lactose is absent, the lac repressor binds to the operator, stopping RNA polymerase from transcribing the genes.
• When lactose is present, it acts as an inducer, binding to the repressor and inactivating it.
• This lets RNA polymerase bind to the promoter and start transcribing the genes to break down lactose.

This is enzyme induction, where lactose triggers the production of enzymes.

Question 2

Comparison

Answer 2

• Lac Operon: Off until lactose turns it on. Lactose helps make enzymes to break it down.
• Trp Operon: On until tryptophan turns it off. Tryptophan stops its own production when there’s enough.
  Lac = Stopped until activated
  Trp = Active until stopped

Question 3

Trp Operon: Enzyme Repression

Answer 3

The trp operon controls the production of tryptophan.

• When tryptophan is absent, the trp repressor is inactive, and RNA polymerase can transcribe the genes to make tryptophan.
• When tryptophan is present, it acts as a corepressor, activating the repressor.
• The active repressor binds to the operator, blocking RNA polymerase from transcribing the genes.

This is enzyme repression, where tryptophan stops the production of more tryptophan when there’s enough.