A compound known as X- Gal is widely used in molecular genetic research. When wild- type normal) E. coli is grown on medium containing X- Gal, the bacterial colonies turn blue. In contrast, when lacZ mutants are grown on medium containing X- Gal, the bacterial colonies remain their normal white colour. What is X- Gal likely to be?
A) a compound chemically similar to glucose
B) a compound chemically similar to lactose
C) a compound chemically similar to galactose
D) a compound that cannot be transported into lacZ mutants
E) a compound that can only be transported into lacA mutants

Question

Quizplus · Accepted Answer

X-Gal is likely to be a compound chemically similar to lactose because it is used to detect the activity of the lacZ gene, which encodes for beta-galactosidase, an enzyme that hydrolyzes lactose. When the lacZ gene is active, the bacteria are able to break down X-Gal and produce a blue pigment. Mutations in the lacZ gene result in a loss of beta-galactosidase activity, and therefore the bacteria cannot break down X-Gal and remain white. X-Gal is not chemically similar to glucose or galactose, and there is no evidence to suggest that it cannot be transported into lacZ mutants or that it can only be transported into lacA mutants.

A Compound Known as X- Gal Is Widely Used in Molecular