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.What is X-Gal likely to be?
A)a compound chemically similar to glucose
B)a compound chemically similar to galactose
C)a compound chemically similar to lactose
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 a substrate for the enzyme β-galactosidase, which is encoded by the lacZ gene. When β-galactosidase cleaves X-Gal, it produces a blue product. LacZ mutants lack functional β-galactosidase, so they cannot cleave X-Gal, resulting in white colonies. This indicates that X-Gal is chemically similar to lactose, which is also a substrate for β-galactosidase.

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