Labs / Biology
Gene Switch (Lac Operon)
This is how a bacterium decides whether to make the enzymes that digest lactose. Tap the lactose and glucose supplies (or use the checkboxes) and watch the repressor let go, the CAP activator dock, and RNA polymerase start transcribing. The graph shows the enzyme level climbing or decaying in response.
Promoter ActiveTranscription 0%Enzyme 0%
What to try
- With no lactose around, what is the repressor doing to the operator — and can RNA polymerase get through?
- Add lactose but keep glucose present. Why does transcription only trickle instead of running full speed?
- Now remove the glucose. What docks onto the CAP site, and how fast does the enzyme level shoot up?
- Switch lactose off after the enzyme is high. How long does the enzyme linger before it decays away?
- Slide the enzyme decay rate up and down — does it change the final steady level, the speed of the response, or both?