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ATP hydrolysis is the primary method the human body uses to chemically release energy to muscles and other systems in the body necessary to sustain life. The chemical Adenosine triphosphate (ATP) is converted to Adenosine diphosphate (ADP) by the loss of a phosphoanhydrous group at the end of the compound, resulting in a release of chemical energy and heat. It is also possible for ADP to be converted one level farther down the molecular chain, to Adenosine monophosphate (AMP) releasing further energy. Under special conditions it is sometimes the case as well that ATP can be directly hydrolyzed to AMP, releasing the energy of two phosphate groups on the end of the molecule in the process instead of just one.
The amount of energy released by ATP hydrolysis can vary based on factors such as the pH or acidic level of blood, and the presence of magnesium, which binds to the byproducts of the reaction. Since the conversion of ATP to ADP can lower the pH level of blood, it has been attributed to cases of lactic acidosis, a condition where reduced oxygen levels in the blood can result in shortness of breath, abdominal pain, and other side effects. Cases of lactic acidosis are often a symptom in exercise physiology, when a large demand for energy is being placed upon muscle groups.
Water is also essential to the reaction for ATP hydrolysis to take place. This is usually not accounted for in energy formulas that explain ATP hydrolysis as it is a neutral medium to the final energy outcome. The release of exothermic energy by ATP hydrolysis can produce ionic compounds of water, such as the hydroxyl ion OH.
Chemical storage of energy in the cells of people is important because its rival, storage of energy by heat or calories alone, is less efficient. Cells must remain at a regulated temperature to function properly. Therefore, ATP hydrolysis is a form of not only chemical energy storage, uptake, and release of energy to the body, but it is also the primary means by which the human body transports energy from organ to organ. The chemical is also quite stable and its breakdown results in relatively large releases of energy as the phosphorous-oxygen bonds in an ATP molecule store roughly 7 kcal/mole of energy each.
Though ATP hydrolysis is essential for healthy cellular respiration and function, it is not the only energy-generating chemical reaction in the body. Creatine phosphate is another phosphate chemical used in the body to create energy. As well, ATP is synthesized by the body for further energy use when someone is sleeping or making very little use of muscular groups. Cells in the body generate ATP through the use of proteins and the oxidation of an enzyme, Nicotinamide Adenine Dinucleotide (NADH), which is derived from the vitamin niacin.