Adenosine Triphosphate (ATP)

**Information:** Adenosine triphosphate is a nucleotide formed from the combination of nitrogen-containing purine base of adenine, ᴅ-ribose sugar component and three phosphates (phosphoric acid residues). The compound with one phosphoric acid residue is called adenosine monophosphate (AMP) and the other one with two phosphoric acid residues is called adenosine diphosphate (ADP).

**General meaning:** ATP is a macro-drug compound which hydrolysis releases a lot of energy due, among other things, to electrostatic repulsions between negatively charged oxygen atoms. Hydrolysis of ATP produces phosphate and ADP while releasing energy: ATP + H₂O → ADP + P (depending on the conditions, even AMP and bisphosphate: ATP + 2H₂O → AMP + P-P, can be produced). The released energy can be used for endergonic reactions.

**Functions in photosynthesis:** Primary phase of photosynthesis results in ATP (ADP + P → ATP + H₂O). The driving force of this reaction is the transmembrane difference in proton concentration. However, in the secondary phase, ATP hydrolysis occurs (ATP + H₂O → ADP + P). The energy released in this reaction is used in biosynthetic reactions (the Calvin Cycle).