Immediate source of energy is

In the living cell, the principal high-energy intermediate or carrier compound is adenosine triphosphate (ATP) The impoance of phosphates in intermediary metabolism became evident with the discovery of the role of ATP, adenosine diphosphate (ADP), and inorganic phosphate (Pi) in glycolysisATP plays a central role in the transference of free energy from the exergonic to the endergonic processesThe intermediate position of ATP allows it to play an impoant role in energy transfer. The high free-energy change on hydrolysis of ATP is due to relief of charge repulsion of adjacent negatively charged oxygen atoms and to stabilization of the reaction products, especially phosphate, as resonance hybridsATP is able to act as a donor of high-energy phosphate to form those compounds below it in Table 11-1. Likewise, with the necessary enzymes, ADP can accept high-energy phosphate to form ATP from those compounds above ATP in the table. In effect, an ATP/ADP cycle connects those processes that generate to those processes that utilize, continuously consuming and regenerating ATP. This occurs at a very rapid rate since the total ATP/ADP pool is extremely small and sufficient to maintain an active tissue for only a few seconds.Ref: Harper&;s Biochemistry, 30th edition, page no: 113