Question

Identify the statements pertaining to the regulatory genes (R), associated with the lac operon that are incorrect.
(i) mRNA is transcribed from the R gene whether lactose is present or not.
(ii) mRNA is transcribed from the R gene only when the lactose is present.
(iii) mRNA is transcribed from the R gene only when the lactose is not present.
(iv) Lactose inhibits the translation or R gene mRNA.
A. (i) and (ii)
B. (ii) and (iii)
C. (iii) and (iv)
D. (ii), (iii) and (iv)

Answer 1

Hint: Operon is a set of interconnected genes that, during transcription, combine to form a single messenger RNA molecule and include both structural and regulatory genes (such as an operator and promoter).

Complete step by step solution:
An operon is a collection of genes that are collectively transcribed to produce a single messenger RNA (mRNA) molecule that in turn codes for numerous proteins. In prokaryotes, this type of polycistronic mRNA is commonly seen. The lac operon is a single-promoter operon, or collection of genes (transcribed as a single mRNA). The operon's genes produce proteins that enable the bacterium to utilize lactose as a fuel source. The lactose operon, sometimes called the lac operon, is a collection of genes present in E. coli and other bacteria that are dedicated to the uptake and processing of lactose. The regulating gene is constitutively active in the lac opeon model. The presence of an inducer renders its translation product (repressor) inactive (lactose).
In many enteric bacteria, including Escherichia coli, the lac operon is an operon that controls the metabolism of lactose. It is an operon that is induced. Promotor, operator, three structural genes, and terminator are all present.
LacZ, LacY, and LacA are the three structural genes. The genes lacZ, lacY, and lacA all code for the enzyme beta-galactosidase, beta-galactoside permease, and beta-galactoside transacetylase, respectively. Galactose is split into glucose and galactose by the enzyme A-galactosidase. Lactose sugar is transported into the cell with the aid of permease. An acetyl group from acetyl-CoA is transferred to -galactosidase with the aid of transacetylase.
So, option (D) is correct.

Note:
Operon, a genetic regulatory system present in bacteria and their viruses and characterized by the clustering along the DNA of genes encoding functionally related proteins. This characteristic enables coordinated control of protein production in response to cellular requirements.