Question

Describe the role of lactose in lac operon.

Answer 1

Hint: The lac operon is an operon, or group of genes with a single promoter (transcribed as a single mRNA). The genes present in the operon encode proteins that allow the bacteria to use lactose as an energy source.

Complete answer:
Lactose operon is an operon which is required for the metabolism and transport of lactose in E.coli and many other bacteria that is present in it.The lac, or lactose, operon is only found in E. coli and some other enteric bacteria.
The allolactose is the isomer of lactose and small amounts of allolactose are produced when lactose enters E.coli.
It binds to an allosteric site on the repressor protein which results in a conformational change. As an outcome of this change, the repressor is unable to bind to the operator region and falls off. The RNA polymerase would be able to bind to the promoter and transcribe the lac genes
The allolactose is called an inducer because it turns on, or induces the expression of, the lac genes when necessary.
Presence of lactose (and thus allolactose) helps to determine whether or not the Lac repressor is bound to the operator successfully.
The allolactose binds to an allosteric site which is present on the repressor protein which results in a conformational change. As an outcome, the repressor can no longer bind to the operator region and falls off. The RNA polymerase can then bind to the promoter and transcribe the lac genes.
 At the time when enzymes encoded by the lac operon are produced, they break down lactose and allolactose, eventually resulting in the release of the repressor to stop additional synthesis of lac mRNA.
The messenger RNA breaks down eventually after a very short time.

Note: When glucose is present, the E. coli metabolizes the glucose using alternative energy sources such as lactose, arabinose, galactose, and maltose as a tool.
The glucose is the preferred and most frequently available energy source for E. coli. Enzymes That function to metabolize glucose are made constantly by E. coli.
At the time when both glucose and lactose are available, the genes for lactose metabolism are transcribed at low levels.