Question

Explain the following term in connection with the concept of the lac operon in E.coli:

Repressor

Answer 1

In the lac operon, the repressor is a specific protein that acts as an “off switch” for the gene system. It is continuously produced by the regulatory I gene and has a high affinity for a DNA sequence called the operator.

In the absence of lactose, the repressor binds firmly to the operator, physically blocking RNA polymerase from moving along the DNA. This prevents the transcription of the structural genes, ensuring the cell doesn’t waste energy making enzymes it doesn’t need. When lactose is introduced, it acts as an inducer by binding to the repressor and changing its shape; this causes the repressor to detach from the operator, finally allowing the genes to be switched “on.”