Question

Operon contains

• A. Operator and regulator genes, and repressor
• B. Operator and regulator genes
• C. Operator and structural genes
• D. Operator gene, regulator gene, repressor, structural genes and promoter gene

Answer 1

The correct option is D Operator gene, regulator gene, repressor, structural genes and promoter gene

Operon
An operon has a coordinated group of genes such as regulator gene, promoter, operator, structural genes that function together as a single unit. It has many structural genes under the control of a single promoter and operator.
Regulator gene
The regulator gene of the lac operon, i.e., lac i, synthesises the repressor protein which switches off the operon. This is because the repressor binds to the operator region of DNA.
Operator
Operator is a genetic sequence that lies adjacent downstream to the promoter region of DNA and regulates the synthesis of RNA from the downstream structural genes.
The repressor protein binds to the operator region and helps to switch off the operon. This is because the RNA polymerase cannot bind properly to the promoter which has overlaps with the operator region.
Promoter
Promoter is the sequence of DNA that serves as the site for initial binding of RNA polymerase to proceed with transcription.
Structural genes
The structural genes present in lac operon are lac z, lac y and lac a.
The lac z gene codes for β-galactosidase enzyme, lac y gene codes for permease enzyme, lac a gene codes for transacetylase enzyme.
Final answer
(D) Operator gene, regulator gene, repressor, structural genes and promoter gene