A DNA Double Helix
DNA's iconic twisted ladder comes to life: watch a molecular dynamics simulation of the nucleic-acid double helix in the browser.
DNA — deoxyribonucleic acid — is the molecule that carries the genetic instructions for building and operating every living thing. Its double helix, famously deduced by Watson, Crick, Franklin, and Wilkins in 1953, is one of the most recognizable structures in all of science. This page shows a molecular dynamics simulation of that twisted ladder.
Two Strands, One Ladder
Each strand of DNA is a long chain built from four kinds of nucleotides, distinguished by their bases: adenine (A), thymine (T), guanine (G), and cytosine (C). A sugar-phosphate backbone runs along the outside of each strand — the two rails of the ladder — while the bases point inward to form the rungs. The two strands wind around a common axis into the characteristic right-handed double helix, completing one full turn roughly every ten base pairs.
Base Pairing
The rungs are not random. Adenine always pairs with thymine, and guanine always pairs with cytosine, held together by hydrogen bonds — two for an A–T pair and three for a G–C pair. This complementary pairing means that the sequence of one strand completely specifies the other. It is the structural basis of heredity: when the helix unzips, each strand serves as a template to rebuild its partner, so the genetic message can be copied faithfully every time a cell divides.
Why the Shape Matters
The double helix is more than an elegant picture. Tucking the chemically reactive bases inside the helix protects the genetic information, while the regular, repeating backbone lets the molecule be packed, read, and copied by cellular machinery. Watching the structure flex and vibrate in a molecular dynamics simulation is a reminder that DNA is not a static diagram but a real, jostling physical object — constantly in motion, yet stable enough to preserve a genome for a lifetime. Note: this simulation currently runs slowly, and we are working on speeding it up.
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