The regeneration of ATP from ADP and Pi is fundamental for sustaining cellular activities. This process primarily occurs through oxidative phosphorylation in the mitochondria and substrate-level phosphorylation in the cytosol. In oxidative phosphorylation, the energy from electron transfer is used to drive the synthesis of ATP, while in substrate-level phosphorylation, the transfer of a phosphate group from a high-energy substrate directly phosphorylates ADP to form ATP.
