Question

If bacteria transformed with a recombinant pUC18 plasmid produce white colonies when grown on plates containing ampicillin and Xgal, which of the following is least likely?

a. They produce β-lactamase that provides resistance to ampicillin.
b. They carry a vector that contains a DNA fragment inserted into the multiple cloning site.
c. They produce functional β-galactosidase that cleaves X-gal.
d. They carry a vector with a lacZ gene that has been disrupted and rendered nonfunctional.
e. They carry a vector with the bla gene used as the selectable marker.

Answer 1

c. They produce functional β-galactosidase that cleaves X-gal.

Step-by-step explanation:

β-galactosidase is an enzyme capable of catalyzing the enzymatic hydrolysis of β-galactosides into monosaccharides by hydrolyzing the β-glycosidic bond. On the other hand, X-gal is an analog of lactose composed of galactose, which is widely used in laboratories for the detection of β-galactosidase. In the presence of β-galactosidase, X-gal is hydrolyzed by cleaving its β-glycosidic bond, thereby confirming the presence of β-galactosidase.