Question

Which of the following events would occur in 'Lac-operon' of E. coli when the growth medium has high concentration of lactose ?

• A. The repressor protein binds to RNA polymerase and prevents translation
• B. The inducer molecule binds to repressor protein and RNA polymerase binds to promoter sequence
• C. The structural genes fail to produce polycistronic mRNA.
• D. The repressor protein attaches to the promoter sequence and derepresses the operator

Answer 1

Answer: (B)

Lactose (or allolactose) acts as inducer in Lac operon model. When lactose is present in high concentration in growth medium, it binds to repressor protein, which then fails to bind to operator gene. This results in RNA polymerase binding to promoter region in gene and transcription of structural genes.