## TL;DR

DNA (deoxyribonucleic acid) is the molecule carrying genetic instructions. Watson, Crick, and Wilkins (1953, Nobel 1962) - with crucial X-ray crystallography data from Rosalind Franklin - determined DNA's double helix structure: two antiparallel strands of sugar-phosphate backbone linked by complementary base pairs (A-T, G-C).

## Core Explanation

Nucleotides: Adenine (A), Thymine (T), Guanine (G), Cytosine (C). A pairs with T (2 hydrogen bonds), G pairs with C (3 bonds — stronger). DNA replication: helicase unwinds → DNA polymerase adds complementary bases → two identical copies. Human genome: ~3 billion base pairs, ~20,000-25,000 genes. Central dogma: DNA → RNA (transcription) → protein (translation).

## Further Reading

- [The Double Helix (James Watson, 1968)](https://www.simonandschuster.com/books/The-Double-Helix/James-D-Watson/9780743216302)