Question

Study the given figure and answer the questions:

1. How does the repressor molecule get inactivated?
2. When does the transcription of lac mRNA stop?
3. Name the enzyme transcribed by the gene ‘z’.

Answer 1

1. The repressor molecule gets inactivated when an inducer (such as lactose or allolactose) binds to it. This binding causes a conformational change in the repressor protein, preventing it from attaching to the operator and allowing transcription to proceed.
2. Transcription of the lac mRNA stops when the inducer (lactose) is absent or has been completely metabolised by the cell. Without lactose, the repressor protein remains active, binds to the operator (o), and physically blocks RNA polymerase from transcribing the structural genes.
3. The ‘z’ gene codes for the enzyme β-galactosidase, which is responsible for breaking down lactose into glucose and galactose.