ATP

Adenosine 5'-triphosphate, or ATP, is the principal molecule for storing and transferring energy in cells. It is often referred to as the energy currency of the cell and can be compared to storing money in a bank. ATP can be used to store energy for future reactions or be withdrawn to pay for reactions when energy is required by the cell. Animals store the energy obtained from the breakdown of food as ATP. Likewise, plants capture and store the energy they derive from light during photosynthesis in ATP molecules. ATP is a nucleotide consisting of an adenine base attached to a ribose sugar, which is attached to three phosphate groups. These three phosphate groups are linked to one another by two high-energy bonds called phosphoanhydride bonds. When one phosphate group is removed by breaking a phosphoanhydride bond in a process called hydrolysis, energy is released, and ATP is converted to adenosine diphosphate (ADP). Likewise, energy is also released when a phosphate is removed from ADP to form adenosine monophosphate (AMP). This free energy can be transferred to other molecules to make unfavorable reactions in a cell favorable. AMP can then be recycled into ADP or ATP by forming new phosphoanhydride bonds to store energy once again. In the cell, AMP, ADP, and ATP are constantly interconverted as they participate in biological reactions.