Final answer:
Sugars and phosphate groups form the sugar-phosphate backbone of DNA, providing the structure from which the nitrogenous bases extend.
Step-by-step explanation:
The two sides or backbones of the molecule are formed by sugars and phosphate groups. These two components alternate to create the structure known as the sugar-phosphate backbone. In the structure of DNA, the phosphate group of one nucleotide bonds covalently with the sugar molecule of the next, forming a sturdy backbone from which the nitrogenous bases protrude. These bases are held together in pairs by hydrogen bonds, which help form the double-helix structure of DNA.