Adenosine triphosphate (ATP) is considered by biologists to be the energy currency of life. It is the high-energy molecule that stores the energy we need to do just about everything we do. In animal systems, the ATP is synthesized in the tiny energy factories called mitochondria.
Considering the structure of ATP, it has a backbone of an ordered carbon compound, but the part that is really critical is the phosphorous part - the triphosphate. Three phosphorous groups are connected by oxygens to each other, and there are also side oxygens connected to the phosphorous atoms. Under the normal conditions in the body, each of these oxygens has a negative charge, and as you know, electrons want to be with protons - the negative charges repel each other. These bunched up negative charges want to escape - to get away from each other, so there is a lot of potential energy here.
If you remove just one of these phosphate groups from the end, so that there are just two phosphate groups, the molecule is much happier. If you cut this bond, the energy is sufficient to liberate about 7000 calories per mole, about the same as the enegy in a single peanut.
Living things can use ATP like a battery. The ATP can power needed reactions by losing one of its phosphorous groups to form ADP, but you can use food energy in the mitochondria to convert the ADP back to ATP so that the energy is again available to do needed work. In plants, sunlight energy can be used to convert the less active compound back to the highly energetic form. For animals, you use the energy from your high energy storage molecules to do what you need to do to keep yourself alive, and then you "recharge" them to put them back in the high energy state.
Second law concepts