What is a defining feature of restriction enzymes that allows precise cutting?

• A. They cut DNA at random locations
• B. They recognize a specific base sequence and cut
• C. They cut only RNA
• D. They ligate DNA ends

Answer: (B)

Restriction enzymes are defined by their ability to recognize a specific DNA sequence and cut at a precise location within or near that sequence. This sequence-specific recognition makes their cuts predictable and reproducible, producing fragments of known sizes. Many recognition sites are palindromic, so the enzyme reads the same sequence on both strands, which helps ensure a clean, defined cut. Depending on the enzyme, the cut can yield sticky ends with short overhangs or blunt ends with no overhang, and these features are especially useful in cloning because complementary ends can anneal and be joined by ligase. In contrast, cutting DNA at random locations would not give predictable fragments; restriction enzymes do not target RNA, and ligating DNA ends is done by a different enzyme, ligase, not by the restriction enzyme.