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. (a) What antibiotic would you put in an agar plate to ensure that the cells of a bacterial colony contain the plasmid

Answer 1

Answer:

tetracycline

Explanation:

When the DNA insert is ligated in Pstl site, the ampicillin gene is disrupted while tetracycline gene is still intact.

- If the bacterial colony is growth in a medium with only ampicillin, only the cells that contains the plasmid with the insert will grow.

- If the bacterial colony is growth in a medium with only tetracycline, the cells which have incorporated the plasmid will survive. We cannot distinguish between cells with plasmid + insert and plasmid alone.

- If the bacterial colony is growth in a plate with ampicillin + tetracyclin, only the cells with the plasmid without the insert will grow.

Therefore, to ensure that the cells of a bacterial colony contains the plasmid, they have to be seeded in a plate with tetracycline.