DNADoppelhelix

The DNA double helix, sometimes written as DNA Doppelhelix in German-language contexts, is the canonical structure of genetic material in living organisms. It consists of two long polynucleotide strands that coil around a common axis to form a right-handed helix, with a sugar–phosphate backbone on the outside and bases oriented toward the interior.

The strands are antiparallel, one running 5' to 3' and the other 3' to 5'. Bases pair specifically: adenine with thymine (two hydrogen bonds) and guanine with cytosine (three hydrogen bonds), yielding stable, uniform width. Base stacking among adjacent bases further stabilizes the helix.

Geometrically, DNA spans about 3.4 angstroms per base pair, roughly 10.5 base pairs per turn, and about 34 angstroms per turn. The molecule features major and minor grooves that proteins can recognize for regulation and replication.

Under physiological conditions, the dominant form is B-DNA, a right-handed helix. Alternative forms such as A-DNA and Z-DNA can occur with different sequences or hydration levels. In eukaryotes, DNA is packaged into chromatin with histone proteins, enabling compaction and regulation.

Functionally, DNA stores genetic information and directs its own replication and transcription. Through semi-conservative replication, each daughter molecule inherits one original strand and one newly synthesized strand. The sequence of bases encodes genes and regulates cellular processes; DNA-interacting enzymes read and modify this information during replication, repair, transcription, and translation.

The discovery of the DNA double helix in 1953 by James Watson and Francis Crick, building on Rosalind Franklin’s X-ray data and Chargaff’s rules, revolutionized biology and enabled modern genetics, biotechnology, and forensic science.