Adenosine Triphosphate (ATP)
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.

See also: Nucleotides, ATP as Free Energy Currency (from Chapter 12), ADP, AMP, Figure 3.7