Question

The lac operon consists of

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

Answer 1

Answer: (D)

One regulatory gene and three structural genes

Answer 2

The lac operon consists of one regulatorygeneand three structural genes.

The lac operator is a short region of DNA that consists of a promoter, an operator, a regulator gene, and three structural genes z, y, and a. The lac operon interacts with a regulatory protein lac repressor that negatively controls the transcription of the operon. The three structural genes are:

• lac z - codes for the enzyme β-galactosidase. This cleaves the lactose molecule to give glucose and galactose. This enzyme is also responsible for converting lactose to allolactose.
• lac y- codes for the permease that transports lactose into the cell.
• lac a- codes for acetyltransferase (or β-galactoside transacetylase). This particular operon is controlled by both positive and negative regulation.

It was two French scientists, Jacob and Monod who proposed the lac operon of E. coli.

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