Question

Match the column and find out the correct combination:
            Gene Product Function of the product
I. Z-gene beta-galactosidase hydrolysis lactose
II. Y-gene Transacetylase uptake of lactose
III. A-gene Permease protein function not known
IV. Inhibitor gene Repressor protein switch off operator gene
(A) II and III
(B) I and III
(C) I, III and IV
(D) I and IV

Answer 1

Hint: Lac operon is functional in prokaryotes only. It has many cistrons and each cistron codes for its specific protein. The proteins or enzymes synthesised by each cistron of lac operon are used for lactose metabolism. Lac operon consist of i gene, z gene, y gene and a gene. All these genes code for different proteins.

Step by step solution:

Lac operon is basically present in prokaryotes including bacteria. It is a polycistronic DNA (eukaryotes have only monocistronic DNA) which is it has many cistrons. Lac operon consists of I gene that is known as an inhibitor gene (not an inducer) and its codes for repressor protein which is responsible for switching off the operator gene. The structural gene constitutes three genes that are- the Z gene, the Y gene and A-gene.
The Z gene codes for beta-galactosidase which is responsible for the hydrolysis of lactose (also known as beta galactoside). The Y gene codes for permease, which is responsible for increasing the permeability of the cell for beta galactoside or lactose. The gene codes for transacetylase.
The lac A-gene synthesised Galactoside acetyltransferase (thiogalactoside transacetylase). Thiogalactoside transacetylase is an enzyme transferring an acetyl group from acetyl-CoA to galactosides, lactosides, and glucosides.

All the genes present on Lac operon synthesize proteins which are responsible for the metabolism of lactose ( a disaccharide of glucose and galactose). Lactose regulates switching on and off of lac operon, therefore it is termed an inducer.
So, option (D) is correct.
Note: In the lac operon, lactose acts as both substrates as well as inducers. We usually call lactose the inducer of lac operon but the actual inducer is allolactose. Also, note that this process does not occur in eukaryotes and is strictly restricted to prokaryotes only.