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 color. X-gal is likely to be a compound ________.
A) chemically similar to glucose
B) chemically similar to galactose
C) chemically similar to lactose
D) that cannot be transported into lacZ mutants
E) that can be transported only into lacA mutants

Question

Quizplus · Accepted Answer

X-gal is a synthetic compound that is chemically similar to lactose, a sugar that is the natural substrate for the enzyme β-galactosidase. When wild-type E. coli with functional β-galactosidase is grown on medium containing X-gal, the enzyme cleaves X-gal and produces a blue color compound. Mutant strains of E. coli that do not have a functional β-galactosidase enzyme cannot cleave X-gal, and therefore the colonies remain white.

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