deoxyribonucleic

Deoxyribonucleic acid, commonly abbreviated DNA, is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of almost all organisms and many viruses. DNA is a long polymer made of repeating units called nucleotides. Each nucleotide contains a deoxyribose sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).

The backbone is formed by alternating sugar and phosphate groups; the two strands run in opposite directions (antiparallel) and twist to form a double helix. Base pairing rules, discovered by Chargaff and evidenced by X-ray data from Rosalind Franklin, link A with T and C with G through hydrogen bonds, producing complementary strands. The sequence of bases encodes genetic information.

Location and structure vary by organism. In eukaryotes, DNA is mainly in the nucleus, organized into chromosomes, with some in mitochondria and chloroplasts. In prokaryotes, DNA is generally a single circular chromosome in the cytoplasm. The genetic material is highly organized and packaged with proteins to fit inside cells.

Function and central concepts. DNA stores hereditary information and is replicated for cell division (semi-conservative replication). The information is transcribed into RNA, which is translated into proteins, a process known as the central dogma of molecular biology. This framework underlies inheritance, development, and cellular function.

History and impact. The double helix model was proposed in 1953 by James Watson and Francis Crick, based on crystallography data from Rosalind Franklin and Maurice Wilkins, with Chargaff’s base-pairing rules guiding interpretation. Today, DNA sequencing, cloning, forensic science, medicine, and biotechnology rely on the molecule’s properties. Mutations introduce genetic variation and drive evolution.