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: Operon system was proposed by Francis Jacob (a geneticist) and Jacques Monod (a biochemist). It was discovered in bacteria and is a model of gene regulation. The operon consists of a coordinated structure of genes such as structural gene, operator gene, promoter gene, regulator gene. These work together and alter a metabolic pathway as a unit. Some examples of operon are lac operon, trp operon, ara operon, his operon, val operon etc.

Complete answer:
The lac operon (lac refers to lactose) contains one regulatory gene or inhibitor gene (i), one promoter gene, one operator gene and three structural genes. The bacterium that Jacob and Monod used is E. Coli. In E. Coli, breakdown of lactose requires three enzymes. This device is called an inducible system because the addition of lactose itself stimulates the manufacturing of required enzymes.

Lac operon genes:
Structural genes- Three structural genes are: -
Lac z: These genes code for beta-galactosidase which is exceptionally responsible for the hydrolysis of the disaccharide, lactose into its monomeric units’ glucose and galactose.
Lac y: This gene codes for permease, which increases permeability of the cell wall to beta-galactosidase.
Lac a: The gene codes for transacetylase which can transfer acetyl group to beta-galactosidase.

Operator gene: It binds with a protein molecule or regulator molecule, which prevents the transcription of structural genes.
Promoter gene: The gene possess site for RNA polymerase attachment.
Regulator gene (i): This gene codes for a protein known as repressor protein, it is synthesized consistently from the i gene and the functions always.
The operon is switched off when the repressor protein produced by means of regulatory or inhibitory gene binds to the operator gene. Here the RNA polymerase binding site is blocked and consequently there would be no transcription.

Hence, the right answer is choice (B).

Note: We can therefore conclude that chronic diseases are more dangerous than acute diseases and that they need proper care, attention and research because they affect the patient both mentally and physically.