Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow:
| p | i | p | o | z | y | a |
i. Identify and name the regulatory gene in this operon. Explain its role in ‘switching off’ the operon.
ii. Why is lac operon’s regulation referred to as negative regulation?
iii. Name the inducer molecule and the products of the genes ‘z’ and ‘y’ of the operon. Write the functions of these gene products.
i. i gene is the regulatory gene and codes of repressor which acts as inhibitor as inhibits the transcription of structural genes. The repressor of the operon is synthesised from the i gene. The repressor protein in the absence of an inducer (lactose or allolactose) binds to the operator region of the operon and prevents RNA polymerase from transcribing the structural genes. Thus ‘switching off’ the operon.
ii. Regulation by lac operon is referred to as negative regulation because the repressor binds to the operator for ‘switching off’ the operon.
iii. Lactose or allolactose acts as an inducer. Gene z codes for β-galactosidase (gal) enzyme which breaks lactose into galactose and glucose. Gene y codes for permease, which increases the permeability of the cell to lactose.