In microbial world, there is considerable metabolic diversity exist. However, there are several biochemical principles common to all types of metabolism. These principles include: (1) the use of ATP to store energy captured during e ergo is reactions so it can be used to drive endergonic reactions; (2) the organization of metabolic reactions into pathways and cycles; (3) the catalysis of metabolic reactions by enzymes; (4) the importance of oxidation – reduction reactions in the energy conservation.
Energy is released from a cell’s metabolism (cell’s energy source e.g. food) specially catabolism of nutrients. This energy can be stored in ATP, rather then, wasting this energy. ATP is an excellent molecule to store energy in its’ phosphate – phosphate bond. This stored energy can be transferred or reutilized in the anabolic reactions. Because of easiness of transfer energy in the form of ATP, it is called as energy currency of cell. To get ATP, cell do certain processes so that they can “earn” ATP and carry out other processes in which they “spend” their ATP.
Through metabolic processes, ATP is hydrolyzed into ADP, or further to AMP, and free inorganic phosphate groups. While conversion of ATP (Adenosine 5’-triphosphate) to ADP (Adenosine diphosphate) or AMP (adenosine mono phosphate) is energetically favorable, yielding Gibbs-free energy of – 7.3 kcal/mol.
Although the free energy change for the hydrolysis of ATP is quite large, there are numerous reactions that release even greater amounts of free energy. This high energy is used to resynthesizes ATP from ADP and Pi during catabolism or other energy conserving process. Likewise, catabolism can generate molecules with a phosphate group transfer protein tail that is even higher than that of ATP. Cells use these molecules to regenerate ATP from ADP by a mechanism called substrate-level phosphorylation. Thus ATP, ADP and Pi forms an energy cycle.When ATP is hydrolyzed, the energy released drives endergonic process such as anabolism, transport and mechanical work.