Why do you have to use the same enzyme to cut both bacterial and cell DNA?

Answer:To cut DNA, all restriction enzymes make two incisions, once through each sugar-phosphate backbone (i. e. each strand) of the DNA double helix. Sometimes the process is called restrictive digestion.

DNAs have the same backbone structure.

Explanation:

A restriction enzyme, restriction endonuclease, or restrictase is an enzyme that cuts DNA into fragments at or by specific recognition sites within molecules known as restriction sites.

Restriction enzymes belong to the broader class of endonuclease group of enzymes.