Suppose one restriction enzyme (enzyme A) makes two cuts in a circular DNA molecule, and another restriction enzyme (enzyme B) makes one cut in that same DNA.The cuts are not in the same place, and the cut fragments are not exactly the same size.The restriction digestion is set up on an electrophoresis gel.How many bands should the gel pick up if both enzymes A and B are used in the restriction digestion?
A) Two
B) Three
C) Four
D) Five
E) Six

Question

Quizplus · Accepted Answer

When enzyme A makes two cuts in a circular DNA molecule, it linearizes the molecule and then cuts it once more, resulting in two linear fragments. Enzyme B makes one cut, which would linearize the circular DNA if it were intact, but since both enzymes are used together, the single cut by enzyme B will further divide one of the two fragments generated by enzyme A into two smaller fragments. Thus, there will be a total of three fragments and therefore three bands on the gel.

Suppose One Restriction Enzyme (Enzyme A) Makes Two Cuts in a Circular