Question

Select the two correct statements out of the four (a to d) given below about lac–operon:
a) Allolactose may bind with repressor and inactivate it.
b) In the absence of lactose, the repressor binds with the operator regions.
c) The z-gene codes for permease.
d) The i-gene codes for activator protein.

• A. a and d
• B. a and b
• C. a and c
• D. b and c

Answer 1

The correct option is B a and b

Allolactose binds to the repressor, causing it to be released from the operator. In doing so, it induces transcription of the z, y and a structural genes which code for beta-galactosidase, permease and transacetylase respectively. It exerts a positive control in lac operon because in its absence RNA polymerase is unable to recognise promotor gene. In the absence of an inducer (lactose or an analog), the lac repressor binds to the lac operator site and prevents transcription of the lac operon. Most of the effect of lac repressor's binding to the operator is to block the progression of RNA polymerase transcription. The i gene codes for the repressor of the lac operon. Hence, the correct statements are a and b.