Phosphodiester Linkages

Nucleotides consist of a base, a pentose sugar, and a phosphate group.

Nucleotides polymerize when the phosphate group of one nucleotide links to the hydroxyl group of the sugar of another nucleotide through a condensation reaction to form nucleic acids, such as DNA. Each reaction forms an ester bond between the phosphate group and the sugar.

Since there are two ester bonds connecting two nucleotides, this linkage is called a phosphodiester bond.

The first ester bond already exists between the phosphate group and the 5’ carbon atom of the pentose sugar of one nucleotide.

The second ester bond forms between the phosphate group and the 3’ hydroxyl group of the pentose sugar of the preceding nucleotide.

This condensation reaction releases one water molecule as the phosphodiester bond forms.

As more nucleotides are added through phosphodiester bonds, the polynucleotide chain grows to create the sugar-phosphate backbone.