The role of ATP
ATP – adenosine triphosphate – provides an immediate source of energy for all cells in every living organism.
The diagram shows that one ATP molecule is made up of an organic base (adenosine) which is attached to a pentose sugar known as ‘ribose’. This sugar is then attached to three phosphate groups.
A lot of energy is stored in the ATP molecule and this energy is generated by the repulsion between the phosphate group and the negatively charged oxygen atoms which are bonded to each other. Most of the energy is stored in the bond of the last phosphate group and when energy is needed by cells, this bond is broken by a hydrolysis reaction catalysed by the ATPase enzyme. When one molecule of ATP is broken, adenosine diphosphate (ADP) and an inorganic phosphate group (Pi) are produced as well as about 30KJ of energy which is released (this value is measured under laboratory conditions but it is estimated that in cellular conditions, about 50KJ will be released). Although some of this energy is lost as heat, most of it is used by cells in their various biochemical processes. ATP is a more reliable source of energy as it is constantly being resynthesized; it is also a quicker process because only one bond needs to be broken to release energy which is unlike molecules such as glucose.
