dsDNA

Double-stranded DNA (dsDNA) is the molecule that stores genetic information in most organisms and many viruses. It consists of two polynucleotide chains wound into a right-handed double helix. Each chain has a sugar-phosphate backbone and bases—adenine (A), thymine (T), cytosine (C), and guanine (G). Bases on opposite strands pair specifically (A with T, C with G) via hydrogen bonds, creating a stable, complementary structure. The strands are antiparallel, running 5' to 3' in opposite directions, and the canonical form in physiological conditions is B-DNA, about 2 nanometers wide with about 10 base pairs per turn.

Key features include major and minor grooves that interact with proteins involved in replication, transcription, and repair. dsDNA stability depends on base composition, ionic conditions, and hydration; GC pairs form three hydrogen bonds and are more stable than AT pairs. Under some conditions, dsDNA can adopt alternative forms such as A-DNA (more compact) or Z-DNA (left-handed).

Biological role: dsDNA stores information and serves as the template for RNA synthesis. During replication, the two strands separate and are copied semiconservatively by DNA polymerases with the aid of helicases, primases, and ligases. In eukaryotes, dsDNA is organized into chromatin; in bacteria and organelles it often exists as circular DNA.

DNA is subject to damage from environmental agents and metabolism. Repair mechanisms, including base excision repair, nucleotide excision repair, and mismatch repair, help maintain integrity. In research and medicine, dsDNA is central to techniques such as PCR, sequencing, cloning, and various diagnostic assays.