Chemically, DNA consists of two long polymers of simple units called nucleotides, with backbones made of sugars and phosphate groups joined by ester bonds. These two strands run in opposite directions to each other and are therefore anti-parallel. Attached to each sugar is one of four types of molecules called bases. It is the sequence of these four bases along the backbone that encodes information. This information is read using the genetic code, which specifies the sequence of the amino acids within proteins. The code is read by copying stretches of DNA into the related nucleic acid RNA, in a process called transcription.

Within cells, DNA is organized into long structures called chromosomes. These chromosomes are duplicated before cells divide, in a process called DNA replication. Eukaryotic organisms (animals, plants, fungi, and protists) store most of their DNA inside the cell nucleus and some of their DNA in organelles, such asmitochondria or chloroplasts.In contrast, prokaryotes (bacteria and archaea) store their DNA only in the cytoplasm. Within the chromosomes, chromatin proteins such as histones compact and organize DNA. These compact structures guide the interactions between DNA and other proteins, helping control which parts of the DNA are transcribed

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.

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, based upon the crucial X-ray diffraction image of DNA (labeled as "Photo 51") from Rosalind Franklin in 1952,followed by her more clarified DNA image with Raymond Gosling, Maurice Wilkins, Alexander Stokes and Herbert Wilson, as well as base-pairing chemical and biochemical information by Erwin Chargaff.

Crick, Wilkins and Watson each received one third of the 1962 Nobel Prize in Physiology or Medicine for their contributions to the discovery.(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 whichbase pair together. A single turn of the helix constitutes ten nucleotides. The double helix structure of DNA contains a major groove and minor groove, the major groove being wider than the minor groove. 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.

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

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

• Double helix, the structure of DNA

• Double Helix Nebula, a gaseous nebula in the Milky Way Galaxy
  
  • Double Helix Games, a video game developer
  • Soldier of Fortune II: Double Helix, a video game
  • Double-Helix, an alien race in the Wing Commander series
  • Doublehelix, a character in the animated film Asterix and the Vikings
  • Double Helix, an animation group
    
    • The Double Helix, a book about the discovery of the double-helical structure of DNA
    • Double Helix, a 2004 novel by Nancy Werlin
    • Star Trek: Double Helix, a six-book miniseries and a spinoff of the Star Trek: The Next Generation book series
      
      • Double Helix: Double or Nothing, a book in the aforementioned series