Question

What effect would you expect if gene expression of the lac operon was completely reversed?
A. The cell would be more efficient without wasting' the energy required for the low level of Lac Z, Lac Y, and Lac A gene expression.
B. Allolactose would accumulate within the cell and become toxic.
C. Lactose would not be converted into the inducer and the operon could not be induced.
D. All of the above

Answer 1

Hint: 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.

Complete step by step solution:
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. Several other enteric bacteria, including E. coli, contain the lac, or lactose, operon. The genes in this operon produce proteins that are responsible for bringing lactose into the cytosol and breaking it down into glucose.
The regulator gene R creates a repressor protein that binds to the operator site and stops structural genes from being transcribed when inducer lactose is absent, which is the mechanism behind the lac operon. Lactose, an inducer, attaches to the repressor when it is added to the medium, preventing it from binding to the operator.
A low level of Lac z expression is required for conversion of lactose to the inducer, allolactose.
So, option (C) is correct.

Note:
Operons are groups of genes that are managed collectively. François Jacob and Jaques Monod first introduced the operon paradigm for regulating bacterial genes using the negatively regulated lactose genes of E. coli as an example.