DNA is composed of two chains of nucleotides that are coiled together to form a double helix structure. Each chain consists of a sequence of nucleotides made up of a sugar, a phosphate group, and a nitrogenous base. The two strands run antiparallel to each other and are held together by hydrogen bonds between complementary nitrogenous bases on each strand—adenine pairs with thymine, and cytosine pairs with guanine.
The double-helix arrangement is fundamental for the stability of the DNA molecule and is critical for its function, including replication and the encoding of genetic information. The presence of only two strands allows for the formation of specific base pairings, which is crucial for maintaining the integrity of genetic information during cell division and protein synthesis.
While some other nucleic acids, such as RNA, can exist as single strands, DNA's characteristic double-stranded structure is integral to its role in biology, thus making the number of coiled nucleotide chains in DNA specifically two.