The structure of DNA is best described as a double helix. It consists of two strands of nucleotides, which are twisted around each other to form a helix shape. Each nucleotide consists of a nitrogenous base, a deoxyribose sugar, and a phosphate group. The nitrogenous bases are adenine (A), thymine (T), guanine (G), and cytosine (C). These bases pair up with each other in a specific way: A with T, and G with C. This pairing is known as complementary base pairing.

The double helix structure of DNA was first proposed by James Watson and Francis Crick in 1953. Their model was based on X-ray crystallography data collected by Rosalind Franklin and Maurice Wilkins. The double helix model has since become the accepted model for the structure of DNA.

The double helix structure of DNA is important for a number of reasons. It allows for the storage of genetic information in a compact and efficient way. It also allows for the replication of DNA, which is essential for cell division and growth. The double helix structure also provides a mechanism for gene regulation, which allows cells to control which genes are expressed.