What are restriction enzymes and how are they used?

Restriction enzymes (restriction endonucleases) are bacterial enzymes that cut DNA at specific recognition sequences, typically 4-8 base pairs long. They serve as a bacterial defense mechanism against viral DNA. Type II restriction enzymes, most commonly used in molecular biology, cut at or near their recognition sites producing either blunt ends or sticky (cohesive) ends with overhangs. They are essential tools for DNA cloning, mapping, and genetic engineering, allowing precise cutting and recombination of DNA fragments.