Adenosine triphosphate (ATP) is the primary molecule for storing and transferring energy in cells. It is often referred to as the "energy currency" of the cell, as it provides readily releasable energy in the bond between the second and third phosphate groups. The breakdown of ATP through hydrolysis serves a broad range of cell functions, including signaling, DNA/RNA synthesis, and muscle contraction. ATP is synthesized from multiple catabolic mechanisms, including cellular respiration, beta-oxidation, and ketosis. The key functions of ATP in cells include:

• Energy source: ATP captures chemical energy obtained from the breakdown of food molecules and releases it to fuel other cellular processes.

• Shuttle: ATP serves as a shuttle, delivering energy to places within the cell where energy-consuming activities are taking place.

• Phosphorylation: ATP powers cellular processes by transferring a phosphate group to another molecule, a process called phosphorylation.

• Extracellular signaling: ATP is an important extracellular signaling molecule, acting as a neurotransmitter in both peripheral and central nervous systems).

In summary, the function of ATP is to provide energy for cellular processes, shuttle energy within the cell, and act as an extracellular signaling molecule.