The main function of ATP (adenosine triphosphate) in cells is to serve as the primary energy currency. ATP stores and releases energy as needed for various biological processes, including muscle contraction, cellular respiration, and biochemical reactions. When cells require energy, ATP is hydrolyzed to ADP (adenosine diphosphate) and inorganic phosphate, releasing energy that fuels cellular activities. Understanding ATP is essential for studying metabolism and energy transfer in living organisms.