Question

Study the figure given below and answer the following questions.(i) Name the molecule ‘X’ synthesised by ‘i’ gene. How does this molecule get inactivated?
(ii) Which one of the structural genes codes for E-galactosidase?
(iii) When will the transcription of this gene stop?

Answer 1

1= repressor protein
2.z structural gene codes
3.when repressor protein bind to the operator

Answer 2

Answer:

(i) The molecule X synthesized by the I gene is the repressor.

(ii) The structural gene- z codes for the enzyme galactosidase.

(iii) The transcription of the genes stops when the repressor molecule binds onto the operator(o).

Explanation:

This is a lac operon that needs an inducer as well as an activator to activate the transcription of the structural genes beyond the threshold level.

The same operon also has a negative regulatory mechanism and hence produces a repressor molecule normally that binds to the operator and turns off the transcription of the structural genes.

In order to inactivate the repressor molecule, an inducer( such as lactose) needs to be present that binds to the repressor and prevents it from blocking the operator of the operon.