Question

What does the wild-type lacI protein do? a. Acts as a repressor (inhibits transcription from the lac operon). b. Acts as an inducer (induces transcription from the lac operon). c. Recruits RNA polymerase to the lac promoter. d. Recruits RNA polymerase to the lac operator. e. Acts as an inducer (induces transcription from the lac operon) and recruits RNA polymerase to the lac promoter.

Answer 1

Acts as a repressor (inhibits transcription from the lac operon)

Answer 2

Answer:

a. Acts as a repressor (inhibits transcription from the lac operon)

Explanation:

LacI is a repressor protein that plays an important role in lac operon. Lac operon is usually switched off i.e. it is inactive in absence of lactose and presence of glucose. The operon has an operator region, promoter region and structural genes.

In absence of lactose, LacI repressor binds to the operator area. Since operator region overlaps with the promoter region, RNA Polymerase is not able to bind to promoter due to presence of repressor. Transcription of lac operon genes does not take place. When lactose is present, some of it is converted into allolactose. Allolactose binds to LacI repressor making it change its shape. The repressor is no longer able to bind to operator region and RNA Polymerase is free to transcribe the genes making the operon active.