<unk>  is the reaction by which chemical energy that has been stored and transported in the high-energy phosphoanhydridic bonds in<unk>  (Adenosine triphosphate) is released, for example in the muscles, to produce work. The product is ADP (Adenosine diphosphate) and an inorganic phosphate, orthophosphate (Pi). ADP can be further hydrolyzed to give energy, AMP (Adenosine monophosphate),  and another orthophosphate (Pi).<unk>  is the final link between the energy derived from food or sunlight and useful work such as muscle contraction, the establishment of ion gradients across membranes, and biosynthetic processes necessary to maintain life.<unk>  of the phosphate groups in<unk>  is especially exergonic, because the resulting orthophosphate group is greatly stabilized by multiple resonance structures, making the products (ADP and Pi) much lower in energy than the reactant <unk> . The high negative charge density associated with the three adjacent phosphate units of<unk>  also destabilizes the molecule, making it higher in energy.<unk>  relieves some of these electrostatic repulsions as well, liberating useful energy in the process.<unk>  of the terminal phosphoanhydridic bond is a highly exergonic process, producing -30.5 kJ mol-1 energy. This reaction can then be coupled with thermodynamically unfavorable reactions to give an overall negative (spontaneous) ΔG for the reaction sequence. The actual value of ΔG for<unk>  varies, primarily depending on Mg2+ concentration, and under normal physiologic conditions is actually closer to -50 kJ mol-1.
In humans, approximately 60% of the energy released from the<unk>  of one mole of<unk>  produces metabolic heat rather than fuel the actual reactions taking place.
File:ATP structure.svg
Source: A biochemistry test at medical university Karolinska Institutet, Stockholm, Sweden 2005.
ATP hydrolysis
Phosphorylation cascade
Oxidative phosphorylation
Cellular respiration
Fatty acid metabolism
Edman degradation
Chiral pool synthesis
Signal transduction