How to Identify Escherichia coli Cells that Do Not Grow on Tetracycline Medium
Which of the following Escherichia coli cells did NOT produce colonies on the growth medium containing tetracycline?
a. Cells that picked up a plasmid without any foreign genes.
b. Cells that did not pick up a plasmid.
c. All of these types of cells produced colonies.
d. Cells that picked up a recombinant plasmid containing another gene.
e. Cells that picked up a recombinant plasmid containing the ribosomal DNA gene.
Final answer:
The E. coli cells that did not grow on a medium containing tetracycline are those that picked up a recombinant plasmid with a disrupted tetracycline resistance gene.
Explanation: The Escherichia coli cells that did NOT produce colonies on the growth medium containing tetracycline are cells that picked up a recombinant plasmid containing another gene, where the gene for tetracycline resistance was inactivated. In this scenario, the recombinant plasmid used was likely pBR322, which carries two antibiotic resistance genes; one for ampicillin and the other one for tetracycline. If these E. coli cells picked up a recombinant plasmid where the tetracycline resistance gene was disrupted during the insertion of another gene, they would not survive on a growth medium containing tetracycline. However, they may still exhibit resistance to ampicillin if the ampicillin resistance gene is intact.
In contrasting cases, untransformed cells that failed to take up a plasmid will not grow on a medium containing ampicillin due to the lack of the ampicillin resistance gene. Such selectivity allows for the identification of cells that have successfully been transformed with the plasmid vector.
In blue-white screening, blue colonies typically represent cells with non-recombinant plasmids containing a functional lacZ gene, which allows for the identification of cells that have taken up plasmids without the desired gene insert.