The genetic material of most living organisms, which is a major constituent of the chromosomes within the cell nucleus and plays a central role in the determination of hereditary characteristics by controlling protein synthesis in cells (see also genetic code). It is also found in chloroplasts and mitochondria (see extranuclear genes; mitochondrial DNA). DNA is a nucleic acid composed of two chains of nucleotides in which the sugar is deoxyribose and the bases are adenine, cytosine, guanine, and thymine (compare RNA). The two chains are wound round each other and linked together by hydrogen bonds between specific complementary bases (see base pairing) to form a spiral ladder-shaped molecule (double helix; see also supercoiling). See illustration.
When the cell divides, its DNA also replicates in such a way that each of the two daughter molecules is identical to the parent molecule (see DNA replication). See also complementary DNA.
http://www.dnaftb.org/dnaftb/ An animated primer on basic aspects of DNA, genes, and heredity, produced for the Cold Spring Harbor Laboratory
Molecular structure of DNA
Subjects: Science and Mathematics.