Recombinant DNA, illustration. Two sections of DNA (deoxyribonucleic acid, yellow and purple) from different organisms are cut by restriction enzymes, also known as restriction endonucleases, at a specific site. This leaves overhanging ends on the molecules that are complementary to each other, as the DNA bases guanine (G) and cytosine (C), and adenine (A) and thymine (T) always pair up together. The two overhanging ends can be joined to each other by the enzyme DNA ligase to form a recombinant DNA molecule (bottom).