If bacteria transformed with a recombinant pUC18 plasmid produce white colonies when grown on plates containing ampicillin and X
gal, 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.
c. They produce functional β-galactosidase that cleaves X-gal.
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.
Cancer is caused by changes to certain genes that alter the way our cells function. Some of these genetic changes occur naturally when DNA is replicated during the process of cell division. But others are the result of environmental exposures that damage DNA.
