What is the purpose of growing transformed bacteria in the presence of ampicillin?

What is the purpose of growing transformed bacteria in the presence of ampicillin?

• A. Ampicillin promotes growth of transformed cells.
• B. Ampicillin kills transformed cells.
• C. Only cells with plasmid containing ampicillin resistance can grow; you can select transformed cells.
• D. Ampicillin has no effect on growth.

Answer: (C)

Growing transformed bacteria in ampicillin provides a way to select for cells that actually took up the plasmid. The plasmid you introduce carries an ampicillin resistance gene, so bacteria with the plasmid can defend against the antibiotic and continue to grow. Ampicillin disrupts cell wall synthesis, which would kill most bacteria that lack resistance; only those with the resistance gene survive and form colonies. This selective pressure enriches for transformed cells, allowing you to identify and work with the colonies that likely carry the plasmid. Without antibiotic selection, both transformed and non-transformed cells would grow, making it hard to distinguish the cells that received the plasmid.

Growing transformed bacteria in ampicillin provides a way to select for cells that actually took up the plasmid. The plasmid you introduce carries an ampicillin resistance gene, so bacteria with the plasmid can defend against the antibiotic and continue to grow. Ampicillin disrupts cell wall synthesis, which would kill most bacteria that lack resistance; only those with the resistance gene survive and form colonies. This selective pressure enriches for transformed cells, allowing you to identify and work with the colonies that likely carry the plasmid. Without antibiotic selection, both transformed and non-transformed cells would grow, making it hard to distinguish the cells that received the plasmid.