Adenosine Triphosphate
Adenosine Triphosphate (ATP), molecule found in all living organisms that is the main immediate source of usable energy for the activities of the cells. ATP is built up by the metabolism of foodstuffs in the cell in special compartments called mitochondria. Because the energy-exchanging function of ATP and the catalytic (work-boosting) function of enzymes are intimately connected, ATP is characterized as a coenzyme. The adenosine part of the molecule is made up of adenine, a nitrogen-containing compound (also one of the principal components of the gene), and ribose, a five-carbon sugar. Three phosphate units (triphosphate), each made up of one phosphorus atom and four oxygen atoms, are attached to the ribose. The two bonds between the three phosphate groups are high-energy bonds, that is, they are relatively weak and yield their energy readily when split by enzymes. With the release of the end phosphate group, 7 kilocalories (7 calories, in common usage) of energy become available for