How is DNA structured as a double helix?

The structure of DNA as a double helix consists of two polynucleotide strands that coil around each other. Proposed by James D. Watson and Francis H.C. Crick, this configuration features sugar-phosphate chains running along the exterior of the helix, while the nitrogenous bases are positioned on the inside.1

The two strands run in opposite directions and are held together by hydrogen bonds between complementary base pairs: adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This specific pairing is essential for the helical structure. The most common form, known as B-DNA, is a right-handed helix that completes one turn approximately every 10 base pairs and contains a major and minor groove, which serve as sites for protein interaction.12