Question

In lac operon I gene codes for
(a)Inducer of the lac operon
(b)Repressor of the lac operon
(c)Hydrolysis of disaccharide
(d)Permease

Answer 1

Hint: An operon is a group of structural genes found as a cluster. The lac operon is an important operon that consumes lactose as a nutrient source and is switched on when glucose is absent and lactose is found plenty in the environment.

Complete answer:
In lac operon I gene codes for a repressor protein. The lactose operon also known as the lac operon is an operon needed for the utilization of lactose in a microorganism such as E.coli. Glucose is the favorite energy source for most bacteria, as it is the easiest to break down, but in absence of glucose, the lac operon helps in the effective utilization of lactose through the activity of beta-galactosidase.
The lac operon constitutes an operator, promoter, and other structural genes that are necessary for proper functioning and are controlled by the repressor. The lac operon contains genes that codes for a protein that is needed to obtain and process the lactose from the surrounding. These codes are of various types, coding different proteins such as I, P, O, lac Z, lac Y, and lac A. Of this, the lac I gene codes for a repressor protein that controls everything.

Additional Information: -Bacterial operons are capable of producing many proteins from one mRNA transcript. When lactose is needed as a food source for the bacteria, the three genes of the lac operon can be expressed and their corresponding proteins translated: lacZ, lac Y, and lac A.
-β-galactosidase is the product of the gene lacZ, which breaks lactose, into glucose and galactose which are monomers.
Beta-galactoside permease was transcribed by the Lac Y gene, which is a membrane protein that is embedded in the cell membrane to allow the cellular transportation of lactose into the cell. Galactoside acetyltransferase is coded by lac A.
So, the correct answer is ‘Repressor of the lac operon’.

Note: -Lactose is a disaccharide, a bigger sugar molecule that is formed by two smaller monosaccharides, glucose and galactose.
-The lac repressor coded by the l gene, has four-parts and called a tetramer, with two similar subunits. Every subunit contains a helix-turn-helix (HTH) motif which can bind to DNA.
-For the discovery of Lac operon, François Jacob and André Michel Lwoff won Nobel Prize in 1965 in Physiology and Medicine.