In simple terms
The DNA double helix is the twisted, ladder-like structure of the DNA molecule, discovered in 1953, that explained for the first time how genetic information could be physically stored and accurately copied inside living cells. [1]
How it was discovered
By the early 1950s, scientists knew DNA likely carried genetic information but did not know its physical shape. James Watson and Francis Crick, working at Cambridge University, built physical models to test possible structures, drawing heavily on X-ray diffraction images of DNA produced by Rosalind Franklin and Raymond Gosling at King’s College London, particularly a now-famous image known as Photo 51. [1] In 1953, Watson and Crick published a structure showing two strands of DNA wound around each other in a double helix, connected by pairs of chemical bases that always pair in the same fixed way: adenine with thymine, and cytosine with guanine.
This complementary pairing was the key insight. Because each strand’s sequence precisely determines the sequence of its partner, each strand could act as a template for assembling a new matching strand, immediately suggesting a mechanism for how DNA replicates itself when a cell divides. [2]
Why it matters
The discovery is widely regarded as one of the most significant in the history of biology, opening the door to modern molecular biology, genetic engineering, and eventually technologies like DNA sequencing and genetic testing. [2] Watson, Crick, and Wilkins received the Nobel Prize in Physiology or Medicine in 1962; Franklin had died in 1958 and was ineligible, since the Nobel Prize is not awarded posthumously.
Where you’ll see it
- Genetic testing and DNA sequencing technology
- Forensic science, where DNA matching relies on this structure
- Modern biotechnology and genetic engineering
- Biology education, where the double helix is a standard introductory image
Example
When a cell divides, enzymes unzip the double helix down its middle, and each separated strand is used as a template to build a brand new complementary strand, producing two identical copies of the original DNA.
Often confused with
A gene is a specific segment of DNA that codes for a particular protein or function; the double helix is the overall physical structure of the DNA molecule as a whole, within which many thousands of genes are arranged.
Key facts
- James Watson and Francis Crick published the double helix structure of DNA in 1953, drawing heavily on X-ray diffraction images produced by Rosalind Franklin and Raymond Gosling.1
- The structure shows two strands of DNA twisted around each other, connected by pairs of molecules called bases that always pair in a fixed way: adenine with thymine, and cytosine with guanine.1
- The complementary base pairing immediately suggested how DNA could be copied accurately, since each strand could serve as a template for building a new matching strand.2
- Watson, Crick, and Maurice Wilkins received the Nobel Prize in Physiology or Medicine in 1962 for the discovery; Rosalind Franklin had died in 1958 and was not eligible, since the prize is not awarded posthumously.2
Quick checkWhy did the double helix structure immediately suggest an answer to how DNA copies itself?Show answer
Because its two strands pair up in a fixed, complementary way, so each strand can act as a template that specifies exactly how to build a new matching strand.
Sources
- National Human Genome Research Institute. Deoxyribonucleic Acid (DNA). Undated (accessed 1 November 2026)
- Nobel Prize. The Discovery of the Molecular Structure of DNA. Undated (accessed 1 November 2026)
Editorially reviewed by Last reviewed November 1, 2026Researched and drafted with AI assistanceReport an issue