A Review in Biology & Chemistry:

Adenosine triphosphate (ATP) is considered by biologists to be the energy currency of life. It is the high-energy molecule that stores the energy we need to do just about everything we do. It is present in the cytoplasm and nucleoplasm of every cell, and essentially all the physiological mechanisms that require energy for operation obtain it directly from the stored ATP.
Read more @ http://hyperphysics.phy-astr.gsu.edu/Hbase/Biology/atp.html