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  • Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow : <img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAc8AAAAlCAYAAAAk0GJ7AAAGcUlEQVR4nO2dv2vcSBiG9W9M7XY7d1dttU2a

Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow :


(a) Identify and name the regulatory gene in this operon. Explain its role in ‘switching off’ the operon.
(b) Why is the lac operon’s regulation referred to as negative regulation ?
(c) Name the inducer molecule and the products of the genes ‘z’ and ‘y’ of the operon. Write the functions of these gene products.

 

 

 

 
 
 
 
 

Answers (1)

(a) Regulatory gene in this operon is i gene.
Role of the regulatory gene in switching off operon is as follows:
(1) Regulatory gene codes for the repressor protein of the operon, which is synthesized in constant amounts.
(2) The repressor has an affinity for the operator gene. It
binds to the operator and prevents the RNA polymerase from transcribing the structural genes.
(b) When repressor binds to the operator, the operon is switched off and transcription is stopped. So, it is called a negative regulation.
(c) Lactose is an inducer molecule.
Gene ‘z’ codes for beta-galactosidase, which is responsible for the hydrolysis of lactose into galactose and glucose, y gene codes for permease. It increases the permeability of the cell to lactose.

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Satyajeet Kumar

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