DNA. Computer artwork of a single strand of DNA wrapped around a human figure. DNA (deoxyribo- nucleic acid) is the molecule which carries the genetic code. It is found in all living things, and controls growth and development. DNA normally comprises two sugar-phosphate strands joined by cross-linking bases. Four types of base are found in DNA: adenine (A), thymine (T), guanine (G) and cytosine (C). A only binds to T, and C only binds to G. The order of bases on the strands determines an organism's characteristics. When DNA replicates itself, the strands separate and each builds a strand with the complementary base sequence. This produces two copies of the original strand.