Nucleotides are the subunits that are linked to form nucleic acids. All nucleotides are composed of three parts namely a sugar, a phosphate and a nitrogenous base.
It is the phosphate group that allows nucleotides to link to each other to form a continuous strand.
In DNA, the nucleotides of one strand join to bases on the complementary strand by weak hydrogen bonds.
For each strand, the phosphate of one nucleotide is linked to carbon 3 of the sugar in the next nucleotide by an ester bond, and in this way a DNA polymer is made. The repeating pattern of phosphate , sugar and phosphate again forms the back bone of the DNA molecule.
