ATP: structure, synthesis and hydrolysis

In a nutshell

Adenosine triphosphate (ATP) is an energy currency used in all living organisms. No organism could survive without ATP as the energy used from its break-down powers many cellular processes. This summary describes the structure of ATP, how it is formed and how it is broken down.

ATP

Adenosine triphosphate (ATP) is a universal energy supplier for all living organisms. It is a small and soluble organic molecule that is formed from adenine, ribose and three phosphate ions.

ATP hydrolysis

When a cell requires energy, ATP can be hydrolysed to produce adenosine diphosphate (ADP) and an inorganic phosphate ($$P_i$$). This reaction is catalysed by an ATPase enzyme.

Note: ATPase may also be called ATP hydrolase.

​$$ATP\rightarrow ADP+P_i$$​​

During the reaction, a bond is broken to release $$P_i$$. Between $$30$$ and $$34\ kJmol{^-}{^1}$$ of energy is produced during ATP hydrolysis. This energy can then be used directly in processes such as active transport, muscle contraction and many metabolic reactions. The direct use of ATP in another reaction is called a coupled reaction. 

The $$P_i$$ can be added to another molecule or compound through a process called phosphorylation. Phosphorylation of molecules has an important role in regulating different cellular processes like respiration.

ATP synthesis

The ATP hydrolysis reaction is reversible. The reverse is a condensation reaction and it is catalysed by ATP synthase. The reaction combines ADP and $$P_i$$ to reform ATP. 

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$$ADP + P_i\rightarrow ATP$$

The condensation reaction requires energy ($$30.5\ kJmol{^-}{^1}$$) to reform the bond between ADP and the inorganic phosphate. ​