Question

When a typical restriction enzyme cuts a DNA molecule, the cuts are uneven, giving the DNA fragments single-stranded ends. These ends are useful in recombinant DNA work because

a. they enable a cell to recognize fragments produced by the enzyme.
b. they serve as starting points for DNA replication.
c. the fragments will bond to other fragments with complementary ends.
d. they enable researchers to use the fragments as molecular probes.

Answer 1

The correct answer is c. the fragments will bond to other fragments with complementary ends. Restriction enzymes create sticky ends on DNA fragments that can hydrogen bond with complementary sticky ends from other fragments, which are then permanently joined by DNA ligase.

Step-by-step explanation:

When a typical restriction enzyme cuts a DNA molecule, it often does so at a palindromic site, where the sequence reads the same in the 5' to 3' direction on both strands. There are two types of enzymatic cuts: those that produce blunt ends and those that result in sticky ends. The uneven, or staggered, cuts create sticky ends with exposed, unpaired bases. These single-stranded ends are useful in recombinant DNA work because they can hydrogen bond with complementary sticky ends of another DNA fragment cut with the same enzyme. This annealing allows for the easy insertion of DNA fragments into plasmids, which are often used as vectors in recombinant DNA technology. These sticky ends are then permanently joined by the enzyme DNA ligase. Thus, the correct answer to the question is: c. the fragments will bond to other fragments with complementary ends. This property is exploited in recombinant DNA technology to join DNA fragments from different sources, creating a recombinant DNA molecule.