What are restriction enzymes?

• A. Enzymes that copy DNA molecules.
• B. Proteins that synthesize RNA.
• C. Enzymes that cut DNA molecules.
• D. Lipids that repair membranes.

Answer: (C)

Restriction enzymes are enzymes that cut DNA at specific sequences. They are restriction endonucleases produced by bacteria as a defense against invading phages, and they recognize short, often palindromic sequences in DNA to cleave the backbone. This cutting can create sticky ends with overhangs or blunt ends, which is why these enzymes are invaluable in genetic engineering for joining DNA fragments from different sources. The other descriptions don’t fit because copying DNA is done by DNA polymerase, synthesizing RNA is done by RNA polymerase, and repairing membranes involves lipids rather than DNA cutting.