How Does ADP Become ATP?

LAGUNA DESIGN/Science Photo Library/Getty Images

Adenosine diphosphate becomes adenosine triphosphate when a phosphate molecule is bonded to it. ADP has two phosphate groups, and when an additional phosphate group is added, it becomes ATP.

Energy is required to jump start the reaction from ADP to ATP. The chemical equation is written as ADP + Pi + energy ? ATP, whcih means that adenosine diphosphate plus a phosphate molecule and a jolt of energy yields adenosine triphosphate. This reaction typically occurs in both directions; ATP breaks down into ADP, and ADP rebuilds itself back into ATP.

This process is mostly dependent upon the addition and subtraction of a phosphate molecule and the energy required to bond the phosphate to ADP to form ATP. For instance, in order for a phosphate to bond to ADP, a catalyst is needed. The two-stranded phosphate group of ADP requires energy to bond it to an additional phosphate. When ATP breaks down into ADP, it releases energy. As the energy is released, the three-stranded phosphate bond of ATP is broken into two strands. According to Georgia State University, this process generally occurs with water and is written as ATP + H2O ? ADP + Pi. When ATP is added to water, it yields an ADP molecule and a phosphate. When this reaction happens in the ATP to ADP direction, it is known as hydrolysis.