ATP, Your Rechargeable Battery
The human body transports and stores energy in a number of different forms. The best-known energy storage molecule is fat, which slowly builds up in some parts of the body when there is an excess of food molecules. There are also other molecules, especially carbohydrates, that can be broken down to provide energy, or built up to store excess energy.However, one molecule stands out in this regard because it is involved in virtually every exchange of energy in the body. This is adenosine triphosphate, or ATP. The role of ATP is so ubiquitous that it can be thought of as the "battery" that provides energy for everything that we do. Just as a battery can power either a flashlight or a radio, so can ATP be used to power any activity or physiological process. But ATP is not just an ordinary battery--it is rechargeable.
The key to ATP's usefulness is its three phosphate groups, which are shown in red in the cartoon. The bond between the second and third phosphate groups can be broken to release a small amount of energy, just the right amount to power activities inside a cell--such as those involved in flexing a muscle. In this way, ATP ends up providing all the immediate energy needs in a cell.
After a cell has exerted itself, its ATP is depleted. But the molecule that is left over (called ADP, because it is a "diphosphate," with only two phosphate groups) can be recharged again to produce more ATP. To recharge your ATP, all you have to do is provide an energy source, such as the carbohydrates, fats, and proteins in a cheeseburger. So the next time you need to "recharge your batteries," remember that you are doing just that--although the "batteries" are actually ATP.