Adenosine triphosphate; Molecule responsible for the transfer of chemical energy generated or used in metabolic reactions.

Most chemical reactions of cells are consuming energy; they are fuelled by few energy providing reaction chains (in particular by photosynthesis or by the respiratory chain). The energy is stored and tranferred in the form of high energy bonds between the phosphate groups of ATP (or related molecules).

The use of ATP for transferring energy is an early invention of evolution, as this molecule is used by all known organisms. The structure of the molecule corresponds to the building blocks (nucleotides) of RNA.