Question

Why is Lactose called an inducer in lac operon?

Answer 1

Hint: The lac operon, or collection of genes with a single promoter, is a kind of operon (transcribed as a single mRNA). The operon's genes code for proteins that allow bacteria to utilise lactose as a source of energy. It is also present in some fungal cells. The three structural genes lac z, lac y and lac a code for three different proteinaceous enzymes which metabolize lactose.

Complete answer:
To solve this question one should know whether lac operon is an inducible or repressible operon.
Lac operon is an example of inducible operon in which an inducer binds to an active repressor making it inactive thus keeping the operon switched ON and the lactose is metabolized.
Lactose binds to the repressor protein and inhibits it from binding to the operator; it serves as an inducer of the lac operon. The repressor attaches to the operator and prevents RNA polymerase from binding to the promoter and starting transcription in the absence of an inducer.

Additional information:
The lac operon, also known as the lactose operon, is present in E. coli and other intestinal bacteria. Genes coding for proteins that transport lactose into the cytosol and breakdown it into glucose are found in this operon. The glucose is subsequently converted into energy.
The lac operon, which contains the structural genes lacZ, lacY, and lacA, encodes the genes required to obtain and digest lactose from the local environment. lacZ codes for β-galactosidase, an intracellular enzyme that breaks down the lactose disaccharide into glucose and galactose. Lactoside permease (lacY) is a membrane-bound transport protein that pumps lactose into the cell. lacA is an enzyme that converts acetyl-CoA to \[\beta \]-galactosidase by transferring an acetyl group from acetyl-CoA to \[\beta \]-galactosidase.

Note:
Francois Jacob and Jacques Monod devised the operon model of bacterial gene regulation. Operons are units that include groups of genes that code for related proteins. An operon is made up of four genes: an operator, a promoter, a regulator, and a structural gene.