Question

How is the presence of functional β-galactosidase detected in a yeast cell population?

A) It is detected by pH changes.
B) It is detected by a color change.
C) It is detected because cells expressing it die.
D) It is detected because cells expressing it divide more quickly than cells that do not.
E) It is detected because the active enzyme causes an increase in radioactivity.

Answer 1

The presence of functional β-galactosidase in yeast cells is detected by a color change, specifically blue, when a synthetic substrate such as X-gal is cleaved by the enzyme.

Step-by-step explanation:

Presence of functional β-galactosidase in a yeast cell population is most commonly detected by a color change. This is because β-galactosidase can cleave a synthetic substrate such as X-gal, which produces a color change upon cleavage. Essentially, the substrate is colorless and, when hydrolyzed by β-galactosidase, it releases a blue compound. This metabolic activity can be visually observed on nutrient plates where yeast colonies that express functional β-galactosidase turn blue, allowing for distinction between colonies based on their enzyme activity.

This method of detection is valuable in molecular biology and genetics for various applications, including the blue-white screening process utilized in bacterial transformation with plasmids containing the lacZ gene. When the lacZ gene is functional, blue colonies appear; when it is disrupted by an inserted foreign DNA sequence, resulting white colonies indicate a successful cloning event with the desired recombinant plasmid.