The backbone of deoxyribonucleic acid (DNA) is composed of nucleic acids, which are made up of ribofuranoside units strung together by phosphate esters. These phosphodiester bonds (two ester bonds) create the DNA backbone.

This simple ChemSketch shows the linking of nucleotides in DNA via phosphate ester groups:

Phosphate esters are created when phosphoric acid and an alcohol combine. Here is an example with methanol (alcohol), which can form three esters based on how many moles of methanol are used:

In addition to its role in the backbone of DNA, phosphate groups play a biochemical role in ribosome-substrate interactions and the regulation of cellular processes. The regulation of their formation on key body proteins regulates these processes, and malfunctions in their regulation can result in cancer, diabetes, and even obesity.
Phosphate groups also play a major part in the bending of the DNA backbone, due to the repulsion of the negative charges. Other experimentation concerning the role of phosphate ester groups includes looking at their electrostatic contribution to the free energy of the bent DNA backbone as well as the synthesis of heparin-immobilized polyetherurethanes, whose side groups have hydrolysable ester groups (heparin being a synthetic anti-coagulent).