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What forms the sugar-phosphate backbone of DNA?

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Diagram of a DNA polynucleotide chain showing linked deoxyribose sugars, phosphate groups, and nitrogenous bases (adenine, guanine, cytosine, thymine), with an inset comparing ribose and uracil in RNA. — Nucleic acid A portion of the polynucleotide chain of deoxyribonucleic acid (DNA), with an inset showing the corresponding pentose sugar and pyrimidine base in ribonucleic acid (RNA).

The sugar-phosphate backbone of DNA is formed by alternating sequences of deoxyribose sugar and phosphate groups.123

In the double-helix structure of DNA, these sugar-phosphate chains act as the sides of a twisted ladder, while the nitrogenous bases form the rungs. Each nucleotide subunit within these chains consists of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases (adenine, thymine, guanine, or cytosine). The alternating linkage of these sugar and phosphate components provides the structural stability necessary for DNA to function as the primary carrier of genetic information.312