What shape does a DNA molecule have?

A DNA molecule has a double-helix shape: two long nucleotide strands wind around the same axis like a twisted ladder. The sugar-phosphate backbones form the outer sides, while paired nitrogenous bases form the rungs.

The two strands run in opposite directions, a feature called antiparallel orientation. Their bases connect through complementary pairing, allowing each strand to serve as a template when DNA is copied. This structural arrangement is one reason genetic information can be replicated with such high fidelity.

James Watson and Francis Crick proposed the famous molecular model in 1953, drawing on crucial experimental evidence from Rosalind Franklin, Maurice Wilkins, and others. The phrase “double helix” describes the familiar overall form, especially the common B-DNA structure found under ordinary cellular conditions.

DNA is not locked into one shape in every circumstance. It can also adopt forms such as A-DNA and the left-handed Z-DNA, and it may bend, supercoil, or temporarily separate into single strands. Those variations do not change the standard answer to this basic question: DNA is classically shaped as a double helix.