Definition of Double Helix

The molecule of deoxyribonucleic acid exists in the form of a double-helical structure. The DNA molecule is composed of two strands that are antiparallel in direction and are wound around one another. The backbone of the DNA is made up by the molecules of deoxyribose sugar and phosphate groups. The nitrogenous bases i.e. adenine, cytosine, guanine and thymine are attached to the sugar molecules.

The two antiparallel strands are stabilized by the formation of hydrogen bonds between the complementary bases. Adenine and thymine are held together by two hydrogen bonds whereas cytosine and guanine have three hydrogen bonds present between them. The double-helical structure of DNA was given by Watson and Crick in 1953.