Restriction enzymes are proteins that recognize and cut DNA at specific nucleotide sequences, known as recognition sites. This precise cutting ability allows for the manipulation of DNA fragments in molecular biology and genetic engineering. They create blunt or staggered ends, facilitating the insertion or removal of genes. This makes them essential tools for cloning, gene mapping, and recombinant DNA technology. Their specificity ensures that only targeted DNA sequences are cleaved, enabling controlled genetic modifications.

Reference: Molecular Biology of the Cell, Alberts et al., 6th Edition.