ATP, or Adenosine triphosphate, is a necessary fuel for all cells in the body and functions in three main ways. ATP is crucial in transporting substances between cell membranes, including sodium, calcium and potassium. Additionally, ATP is necessary for synthesis of chemical compounds, including protein and cholesterol. Lastly, ATP is used as an energy source for mechanical work, like muscle use.

Glycolysis is one method of producing ATP and occurs in almost all cells. This process is an anaerobic catabolism of glucose that converts a molecule of glucose into two molecules of pyruvic acid and two molecules of ATP. These molecules are then used as energy by various systems in the body. In eukaryotic organisms, or organisms with a membrane bound nucleus, glycolysis occurs in the cytosol.

Oxidative phosphorylation also produces ATP and is a major producer of ATP in organisms -- 26 out of 30 molecules of ATP generated from glucose are produced through oxidative phosphorylation. In oxidative phosphorylation, ATP is produced when electrons flow from chemicals known as NADH or FADH (nicotinamide adenine dinucleotide and flavin adenine dinucleotide respectively) to oxygen.

Beta oxidation is a process that converts lipids into energy. Part of this process produces ATP, which is then used to produce acetyl CoA. Furthermore, beta oxidation takes place in the mitochondria and is closely related to the conversion of ATP to AMP. Beta oxidation also involves the fatty acid cycle, which resembles the citric acid cycle.

Aerobic respiration is the final way that ATP is formed. Aerobic respiration also uses glucose to produce ATP and as the name indicates, oxygen must be present for the process to occur. Without oxygen, aerobic respiration converts to anaerobic respiration, which only produces 2 ATP compared to aerobic respirations 34. Anaerobic respiration results in lactate build up in animals, or alcohol and carbon dioxide build up in yeast and plants.