Question

Explain the role of different genes in a lac operon, when in a ‘Switched On’ state.

Answer 1

The lac operon is a genetic system in E. coli that regulates the metabolism of lactose. It includes:

• One regulatory gene (i-gene) that produces a repressor protein.
• Three structural genes - z, y, and a.
  • z gene: Produces the enzyme β-galactosidase, which breaks down lactose into glucose and galactose.
  • y gene: Produces permease, an enzyme that increases the cell membrane’s permeability to lactose, allowing it to enter the cell.
  • a gene: Produces the enzyme transacetylase.

All the genes in the operon work together in the same or related metabolic pathway. Each operon has an operator region that controls gene expression. In the lac operon, lactose acts as an inducer. It enters the E. coli cell with the help of permease.

In the presence of lactose (inducer): Lactose binds to the repressor protein and inactivates it. As a result, the repressor cannot attach to the operator region. This allows RNA polymerase to bind to the promoter and start transcription. Consequently, the three structural genes are expressed, and their respective enzymes are produced. These enzymes then act on lactose and convert it into glucose and galactose.