A restriction enzyme is a type of protein that can cut DNA at specific sequences. These enzymes are naturally found in bacteria, where they serve as a defense mechanism against viruses by cutting up foreign DNA. Each restriction enzyme recognizes a particular sequence of nucleotides, allowing scientists to manipulate DNA for various applications. In molecular biology, restriction enzymes are essential tools for cloning, gene editing, and DNA analysis. By cutting DNA at precise locations, researchers can insert, delete, or modify genes, facilitating studies in genetics and biotechnology. This process is crucial for creating recombinant DNA, which is used in producing insulin and other important substances.