How is ADP generated by the cell?

ADP is generated by the de-phosphorylation of ATP.

ADP (adenosine diphosphate) and ATP (adenosine triphosphate) are two energy storehouses in a cell. They both have similar components except that ADP has two phosphate groups attached to the nucleoside and ATP has three phosphate groups.

ATP stores more energy because of the presence of a third phosphate group that is attached through a high-energy bond. When the cell requires energy to accomplish a task, the ATP molecule breaks off its third phosphate group releasing the necessary energy that’s stored in its pyrophosphate bond. The cleaving of the third phosphate group results in the formation of ADP, which has only two phosphate groups.