A staircase in the shape of a double helix, in the Vatican Museum

Image of a DNA chain which shows the double helix replicating itself

In geometry a double helix (plural helices) typically consists of two congruent helices with the same axis, differing by a translation along the axis, which may or may not be half-way.^[1]

The term "double helix" is commonly encountered in molecular biology, where it refers to the structure of DNA. The double-helix model of DNA structure was first published in the journal Nature by James D. Watson and Francis Crick in 1953^[2], based upon the crucial X-ray diffraction image of DNA (labeled as "Photo 51") from Rosalind Franklin in 1952 ^[3], followed by her more clarified DNA image with Raymond Gosling^[4][5], Maurice Wilkins, Alexander Stokes and Herbert Wilson^[6], as well as base-pairing chemical and biochemical information by Erwin Chargaff^{[7][8][9][10][11][12]}.

Crick, Wilkins and Watson each received one third of the 1962 Nobel Prize in Physiology or Medicine for their contributions to the discovery^[13]. (Franklin, whose breakthrough X-ray diffraction data was used to formulate the DNA structure, died in 1958, and thus was ineligible to be nominated for a Nobel Prize.)

The DNA double helix is a right-handed spiral polymer of nucleic acids, held together by nucleotides which base pair together^[14]. A single turn of the helix constitutes ten nucleotides^[14]. The double helix structure of DNA contains a major groove and minor groove, the major groove being wider than the minor groove^[14]. Given the difference in widths of the major groove and minor groove, many proteins which bind to DNA do so through the wider major groove ^[15].

The order, or sequence, of the nucleotides in the double helix within a gene specifies the primary structure of a protein.

The term entered popular culture with the publication in 1968 of his book: The Double Helix: A Personal Account of the Discovery of the Structure of DNA, by James Watson.

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