Question

The product of i gene in lac operon binds to
A. Regulatory gene
B. Operator gene
C. Structural gene
D. None of the above.

Answer 1

Hint:- It is a fragment of a bacterial gene, which found in the E. coli chromosome, this gene consists of a structural gene and regulatory sequences, these regulatory sequences recognized by regulatory gene products.

Complete step-by-step solution:-
Lac operon is also known as operan model, this model was described by Jacob and Mondo in 1961. It is a fragment of a bacterial chromosome, which consists of a structural gene and regulatory genes. This is the best model that helps us to understand the process of gene expression.
- Operator gene or lac operator: It is represented by O, it’s a short region of DNA that lies just before the promoter of a structural gene, the transcription or expression of the structural gene is controlled by the operator gene.
- Lac structural gene: Three structural genes are found on lac operon, lac Z, lac Y, and lac A. Lac Z encode beta-galactosidase, lacy encode permease enzyme, and last one lacZ encoded transacetylase enzyme.
Regulation of expression:

The presence or absence of lactose controls the expression of the structural genes because, in this situation, lactose acts as an inducer. If the lactose sugar present in the medium, so the expression of the structural genes take place, and in the absence of lactose sugar gene expression does not take place, because, in the absence of lactose, regulatory gene (i gene) transcribe and then translated into repressor protein, this repressor protein or product of I gen binds to the operator gene or lac operon when this protein binds to lac operon, it acts as a road blockage for RNA polymerase enzyme and this enzyme not able to reach promoter of structural genes, in such situation structural gene are not expressed, But if lactose sugar present in a medium that has the ability to inhibits this binding, because, after the expression of I gene, lactose binds with this and change the conformation of repressor protein due to this binding, repressor protein can bind with lac operon and there is no blockage for RNA polymerase and the expression of structural genes take place.

Hence, the correct answer to this question is option B.

Note:- All the genes in an operon are expressed as a single unit. This type of arrangement is common in prokaryotic genomes. In this type of arrangement, a single promoter is required to start and regulate the transcription of all genes.