The primary structure of DNA is called the double helix. This structure consists of two long strands of nucleotides twisted around each other, resembling a spiral staircase. Each nucleotide is made up of a sugar, a phosphate group, and a nitrogenous base. The specific pairing of bases—adenine with thymine and cytosine with guanine—forms the rungs of the helix. The double helix configuration is crucial for its ability to store genetic information and facilitate replication and transcription processes in living organisms.