Restriction enzymes (endonucleases) are enzymes that which of the following?

• A. Enzymes that cut DNA. Each enzyme will cut DNA at a specific base sequence
• B. Enzymes that replicate DNA
• C. Enzymes that repair mismatches
• D. Enzymes that transcribe RNA

Answer: (A)

Restriction enzymes are endonucleases that act as molecular scissors for DNA. They recognize specific short DNA sequences and cleave the phosphodiester bonds at or within those sites. Because each enzyme has its own recognition sequence, it cuts DNA only at particular base sequences, producing defined fragments. Many enzymes cut in a staggered way to create sticky ends, while others cut straight through to produce blunt ends; in either case, the key idea is sequence-specific DNA cleavage. This function is distinct from DNA replication (carried out by DNA polymerases), repair of mismatches (mismatch repair systems), or transcription of RNA (RNA polymerase).