The structure of DNA (deoxyribonucleic acid) is often described as a double helix, resembling a twisted ladder. It consists of two long strands made up of repeating units called nucleotides. Each nucleotide contains a sugar, a phosphate group, and a nitrogenous base. The four types of nitrogenous bases are adenine, thymine, cytosine, and guanine, which pair specifically: adenine with thymine and cytosine with guanine. The two strands of DNA are held together by hydrogen bonds between the paired bases, creating the rungs of the ladder. The sugar and phosphate groups form the backbone of the structure, providing stability. This unique arrangement allows DNA to store genetic information and play a crucial role in biological processes such as replication and protein synthesis.