Double helix

The structure of DNA with the two strands of DNA spiraling about one other. The double helix looks something like an immensely long ladder twisted into a helix, or coil. The sides of the "ladder" are formed by a backbone of sugar and phosphate molecules, and the "rungs" consist of nucleotide bases joined weakly in the middle by hydrogen bonds. "The Double Helix" is the title of a excellent book by James Watson telling the story of his and Francis Crick's discovery of the correct model for DNA.

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double helix n a helix or spiral consisting of two strands in the surface of a cylinder that coil around its axis esp the structural arrangement of DNA in space that consists of paired polynucleotide strands stabilized by cross-links between purine and pyrimidine bases compare ALPHA-HELIX, WATSON-CRICK MODEL

dou·ble-he·li·cal -'hel-i-kəl, -'hē-li- adj

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Watson-Crick helix the usual configuration of double-stranded DNA in vivo, being two complementary antiparallel polynucleotide chains coiled into a helix, with the sugar-phosphate backbone on the outside and the two chains held together by hydrogen bonds between pairs of bases. The most common form is the classical right-handed helical B-DNA (q.v.), but alternative forms also exist, such as A-DNA and Z-DNA (qq.v.). See illustration at deoxyribonucleic acid.