Question

Study the given figure and answer the following:

1. Name the molecule ‘X’ synthesised by the ‘i’ gene. How does this molecule get inactivated?
2. Which one of the structural genes codes for β-galactosidase?
3. When will the transcription of this gene stop?

Answer 1

1. The molecule synthesised by the ‘i’ gene (regulatory gene) is the Repressor protein.
   This molecule gets inactivated when an inducer (such as lactose or allolactose) binds to it. This binding causes a change in the repressor’s shape, preventing it from attaching to the operator, which effectively switches the operon “on.”
2. The ‘z’ gene (lacZ) is the structural gene that codes for the enzyme β-galactosidase.
3. Transcription of these genes will stop when the inducer (lactose) is absent. In the absence of lactose, the repressor protein becomes active again and binds to the operator (o), physically blocking RNA polymerase from transcribing the structural genes.