Biological macromolecules are organic compounds, predominantly composed of carbon atoms. The carbon atoms are covalently bonded with hydrogen, oxygen, nitrogen, and other minor elements. There are four major biological macromolecule classes: carbohydrates, lipids, proteins, and nucleic acids.

Most macromolecules are composed of single subunits, or building blocks, called monomers. The monomers combine with each other using covalent bonds to form larger molecules known as polymers.

Conversion of monomers into polymers is an energetically intensive process. Therefore, cells rely on ATP, the energy currency of the cell, to power these biochemical processes. For example, during the conversion of glucose into glycogen, ATP is hydrolyzed into ADP and inorganic phosphate (Pi), and releases free energy. The released inorganic phosphate binds to glucose and converts it into glucose 6-phosphate which is required for glycogen synthesis.

This cycle of ATP continuously breaking down into ADP repeats to power all life's processes. Like a rechargeable battery, ADP is continuously regenerated into ATP by the reattachment of a third phosphate group.