Describe5 marksStandard
A student investigates the regulation of two enzymes in the bacterium Bacillus subtilis. Enzyme P is involved in breaking down the disaccharide lactulose. Enzyme Q is involved in the synthesis of the amino acid histidine. The production of enzyme P is inducible, while enzyme Q is repressible.
The table below shows some features of the two enzyme systems.
| Feature | Enzyme P (inducible) | Enzyme Q (repressible) |
|---|---|---|
| Normal state of operon | Off | On |
| Effector molecule that regulates gene expression | Inducer (lactulose) | Corepressor (histidine) |
| Effect of effector on repressor protein | Binds to and inactivates repressor | Binds to and activates repressor |
| Role of regulatory gene | Codes for repressor protein | Codes for repressor protein |
Describe the differences in the genetic control of inducible and repressible enzyme systems. In your answer, refer to the roles of structural genes, regulatory genes, and repressor proteins. Use the lac operon as an example of an inducible system.