The molecular compound that stores energy in living cells is adenosine triphosphate (ATP). ATP serves as the primary energy currency for cellular processes, enabling biochemical reactions essential for life. It is synthesized during cellular respiration and photosynthesis, where energy from nutrients or sunlight is converted into ATP. When energy is required, ATP releases it through the hydrolysis of its phosphate bonds, converting into adenosine diphosphate (ADP). This cycle of ATP synthesis and hydrolysis powers numerous cellular functions, including muscle contraction, active transport, and biosynthesis, making it indispensable for living organisms.