ADP (Adenosine diphosphate) is derived from ATP (Adenosine triphosphate) through the removal of one phosphate group.
When a cell requires energy to perform tasks, ATP undergoes hydrolysis. This process involves the breaking of a high-energy phosphate bond in ATP. Consequently, one phosphate group is released, transforming ATP into ADP and inorganic phosphate (Pi). The energy released during this process is then utilized by the cell to power various cellular activities.
In simpler terms, think of ATP as the cell's primary energy currency. When the cell "spends" energy, it breaks down ATP into ADP and phosphate. Therefore, ADP is essentially what remains after ATP has released some of its energy. The process is reversible; ADP can be converted back into ATP through the addition of a phosphate group, requiring an input of energy. This recharging process occurs during cellular respiration.
Therefore, the direct precursor of ADP is ATP.
