Nucleotides help form the backbone of DNA and RNA.
Nucleotides are subunits that are linked to form nucleic acids. All nucleotides are composed of three parts: a five carbon sugar, a phosphate and a nitrogen - rich structure called a nitrogenous base.
It is the phosphate group that that makes the nucleotide so critical in DNA structure. By linking the phosphate of one nucleotide to carbon 3 of the sugar in the neighboring nucleotide, a DNA polymer is made. The repeating pattern of phosphate, sugar, then phosphate again is commonly referred to as the backbone of the DNA or RNA molecule.