Question

Explain the concept of an operon.

Answer 1

Concept of operon:

The concept of the operon was first proposed by Jacob and Monod. A unit of genetic material that functions in a coordinated manner by means of a regulator, an operator, a promoter, and one or more structural genes that are transcribed together is called an operon. The clusters of genes with related functions are called operons.

Components of an operon:

1. Regulator gene:
   1. This gene controls the operator gene in cooperation with an inducer present in the cytoplasm.
   2. The regulator gene precedes the promoter gene. It may not be present immediately adjacent to the operator gene.
   3. The regulator gene produces a protein called the repressor protein.
   4. The repressor binds with the operator gene and represses (stops) its action. Therefore, it is called a regulator protein.
2. Promoter gene:
   1. This gene precedes the operator gene. It is present adjacent to the operator gene.
   2. RNA polymerase enzyme binds to the promoter gene.
   3. The promoter gene base sequence determines which strand of DNA acts as a template.
   4. When the operator gene is turned on, the enzyme moves over the operator gene, and transcription of the structural genes starts.
3. Operator gene:
   1. This gene lies adjacent to the structural genes and controls their functioning.
   2. When the operator gene is turned on by an inducer, the structural genes produce mRNA.
   3. The operator gene is turned off by a product of the repressor gene.
4. Structural gene:
   When lactose is added to the E. coli culture, the structural genes produce mRNA, which in turn produces polypeptides on the ribosomes.
   

   Structural Gene	Enzyme produced	Function
   lac z	β-galactosidase	\[\ce{Lactose →[β-galactosidase] Glucose + Galactose}\]
   lac y	Permease	Entry of lactose into the cell
   lac a	Transacetylase	Transfers the acetyl group from Acetyl CoA to β-galactosidase