Estrella Mountain Community College, 2000. Scientific American . Biology, Third Edition . Cell Movements . All of the biosynthesis activities of the cell, many of its transport processes and a variety of other activities require energy.
Energy is defined as the capacity to do work.
ATP is built up by the metabolism of food in cell's mitochondria. ATP is characterized as a coenzyme because the energy exchanging function of ATP and the catalytic function of enzymes are intimately connected. ATP is made up of the nitrogenous base adenine, the five-carbon sugar ribose and three phosphate groups. The two bonds between the three phosphate groups are relatively weak and yield their energy readily when split by enzymes. Inside a cell the ATP molecule is split at one of the high energy bonds, releasing the energy to power cellular activities.