Question

A linear piece of DNA has the following restrictions sites: Xbal Noti Psti EcoRi 2 kb 4 kb -> 1 kb 2 kb 3 kb You decided to set up an experiment where you added one of these restriction enzymes to this DNA. After this DNA was digested with that restriction enzyme, you separated the resulting fragment(s) using agarose electrophoresis. After the gel was stained with ethidium bromide, you observed the following gel (the DNA ladder is your reference standard and is comprised of a series of DNA fragments of known length).

Answer 1

Question a

Answer: The results of the gel electrophoresis showed two band of 7kb and 5 kb size. Digestion of the linear DNA with PstI restriction enzyme will generate two fragments of 7kb and 5 kb size. Digestion with other enzymes will to generate those fragments. Hence, PstI restriction enzyme s the correct answer (See the below figure).

Pstl 7 Kb 5 Kb

Question b

Answer: Restriction enzymes recognizes certain sequence called as restriction sites and cut the DNA at that sites. Each restriction enzyme have unique restriction sites.

Restriction sites are usually 4-8bp in length and are palindromic sequence.

For example, restriction enzyme BamHI recognizes G^GATCC restriction site and cuts the DNA at that site.