Final answer:
DNA is composed of repeating units known as nucleotides, which include a phosphate group, a five-carbon sugar called deoxyribose, and a nitrogenous base. These nucleotides form the double helix structure of DNA with the sugar-phosphate backbones and paired nitrogenous bases.
Step-by-step explanation:
The repeating structural units that make up DNA are called nucleotides. DNA is composed of about 3 × 10⁹ nucleotides, which can be broken down into three components: phosphoric acid (H3PO4), a pentose sugar, and a nitrogenous base. The five-carbon sugar found in DNA is termed deoxyribose, which is bonded to a phosphate group and a nitrogenous base to form each nucleotide. The sugar is essential in the sugar-phosphate backbone of DNA's double helix structure.
The double helical structure of DNA is characterized by two strands running antiparallel to each other, with the sugar-phosphate backbones on the outside and the nitrogenous bases on the inside, paired through hydrogen bonding.