Catabolic reactions are breakdown reactions that reduce large molecules to smaller components, releasing energy. Digestion and cell respiration are primarily catabolic processes. Anabolic reactions are synthetic reactions that produce larger molecules from small ones, storing energy in chemical bonds. Photosynthesis and the manufacture of proteins are examples of anabolic processes. Metabolic pathways, both anabolic and catabolic, are chains of reactions involving multiple steps.
Potential energy is stored in the chemical bonds of molecules.
This energy is released when the chemical bond is broken. Some compounds contain high energy bonds. The high-energy bond is the one between the last two phosphate groups. This bond has high energy because both of the phosphate groups contain several oxygen atoms, and the electronegative oxygen atoms tend to pull electrons toward themselves. The resulting tension produces a high energy condition.