What happens when ATP is turned into ADP?
The basic form of energy our cells utilize is ATP.
Some background first...
During cellular respiration (which is not important in this context really) the mitochondria forms ATP which stands for adininetriphosphate. The mitochondria does this by adding a third phosphate to the ADP (adininediphosphate) molecule. This is why the mitochondria is called the "powerhouse of the cell". The ATP molecule is an exceptional molecule at storing energy in the phosphate bonds. For example the ATP can hold about 7000 calories worth of energy per mol of molecules.
Okay now to the fun part. After the mitochondria forms the ATP, this molecule is in the form for the cell to use to preform a variety of important functions throughout the cell. Once the ATP is used, one of the phosphate groups is split off and the ATP is turned into ADP.