ATP serves
as the general "free energy currency" for virtually
all cellular processes. Hydrolysis of ATP is used to drive
countless biochemical reactions, including many that are not phosphorylations.
It is a direct source of energy for cell motility, muscle contraction,
and the specific transport of substances across membranes. The
processes of photosynthesis and metabolism of nutrients are used
mainly to produce ATP. It is probably no exaggeration to
call ATP the single most important substance in biochemistry.
The average adult human generates enough metabolic
energy to synthesize his or her own weight in ATP every
day.
ATP is produced in the cell from ADP as a result of three types of phosphorylations - substrate-level phosphorylations, oxidative phosphorylation, and, in plants, photosynthetic phosphorylation.
ATP is a source of phosphate energy for synthesis of the other nucleoside triphosphates via the reaction that follows:
ATP + NDP <=> ADP + NTP (catalyzed by Nucleoside Diphosphokinase)
ATP is also an allosteric effector of many enzymes.