Question

The lac operon consists of which of the following:

• A. Three regulatory genes and three structural genes
• B. Four regulatory genes only
• C. Two regulatory genes and two structural genes
• D. One regulatory gene and three structural genes

Answer 1

The correct option is D

One regulatory gene and three structural genes

The correct option is option D.

Explanation of the correct option:

1. There are three structural genes in the lac operon namely lac-Z, lac-Y, and lac-A.
2. These genes code for the enzymes $\beta$galactosidase, lac permease, and transacetylase.
3. These genes are located in a linear sequence in the bacterial chromosome.
4. The operon also contains a regulator gene that lies outside the operon and produces the repressor substance.
5. This repressor binds to the operator gene and suppresses the transcription of structural genes.

Explanation of the incorrect options:

Option A:

1. It contains only one regulator gene that codes the repressor.
2. There are three structural genes that code for $\beta$galactosidase, lac permease, and transacetylase.

Option B:

It contains three structural genes namely lac-Z, lac-Y, and lac-A.

Option C:

1. It contains only one regulator gene that codes the repressor.
2. There are three structural genes that code for $\beta$galactosidase, lac permease, and transacetylase.

Final answer: The lac operon consists of one regulatory gene and three structural genes.