ATP (Adenosine triphosphate) is the energy currency in living organisms.
ATP is generated from ADP and phosphate ions by a complex set of processes occurring in the cell.
ATP is manufactured as a result of several cell processes including fermentation, respiration and photosynthesis. Most commonly the cells use ADP as a precursor molecule and then add a phosphorus to it. In eukaryotes this can occur either in the soluble portion of the cytoplasm (cytosol) or in special energy-producing structures called mitochondria.
Charging ADP to form ATP in the mitochondria is called chemiosmotic phosphorylation. This process occurs in specially constructed chambers located in the mitochondrions inner membranes.