ADP consists of three important structural components: a sugar backbone attached to adenine and two phosphate groups bonded to the 5 carbon atom of ribose.

For this reason, biological processes have evolved to produce efficient ways to replenish the potential energy of ATP from ADP.

[3] ADP can be converted, or powered back to ATP through the process of releasing the chemical energy available in food; in humans, this is constantly performed via aerobic respiration in the mitochondria.

[3] Animals use the energy released in the breakdown of glucose and other molecules to convert ADP to ATP, which can then be used to fuel necessary growth and cell maintenance.

ADP and phosphate are needed as precursors to synthesize ATP in the payoff reactions of the TCA cycle and oxidative phosphorylation mechanism.

[7] The enzymes necessary to break down glucose are found in the cytoplasm, the viscous fluid that fills living cells, where the glycolytic reactions take place.

[10] The energy released when electrons are passed from higher-energy NADH or FADH2 to the lower-energy O2 is required to phosphorylate ADP and once again generate ATP.

[citation needed] Under normal conditions, small disk-shape platelets circulate in the blood freely and without interaction with one another.