Question

A plasmid that encodes resistance to ampicillin and tetracycline is digested with the restriction enzyme PstI, which cuts the plasmid at a single site in the ampicillin-resistance gene. The DNA is then annealed with a PstI digest of human DNA, ligated, and used to transform E. coli cells. What antibiotic-resistance phenotype(s) (characteristics) will be found on the plate

Answer 1

Answer: Tetracycline.

Explanation:

A plasmid is a small circular DNA molecule found in bacteria that is separate from the bacterial chromosome and replicates independently of it. They encode for certain genes that play a key role in antibiotic resistance. Restriction enzymes are endonucleases that catalyze the cleavage of phosphodiester bonds in different regions located within a DNA strand. PstI is an example of an endonuclease, it is a type II restriction enzyme produced by the microorganism Providencia stuartii that possesses a restriction target in double-stranded DNA dependent on an unmethylated, palindromic, asymmetric sequence, and in this example, it cuts the plasmid at a single site in the ampicillin-resistance gene. After that, the DNA is annealed with another fragment of DNA and this new recombinant molecule is used to transform E. coli cells. Transformation is a key step in DNA cloning because it occurs after restriction enzyme digestion and ligation treatments and transfers newly made plasmids into bacteria. So these bacterias will have a new fragment of DNA, which still has a tetracycline resistance gene but it no longer has the ampicillin resistance gene because it was disrupted by the restiction enzyme. Thereby, the antibiotic resistance phenotype is the tetracycline resistace.