Endonucleases are enzymes that cut the phosphodiester bonds within a nucleic acid strand, such as DNA or RNA. They play a crucial role in various biological processes, including DNA repair, replication, and recombination. By cleaving the nucleic acid at specific sites, endonucleases help maintain the integrity of genetic information. These enzymes can be classified into different types based on their function and specificity. For example, some endonucleases are involved in the immune response, while others are used in laboratory techniques like restriction enzymes for cloning and genetic engineering. Their ability to target specific sequences makes them valuable tools in molecular biology.