... by highly specific enzymes. When only one phosphoryl group is added to the ribose sugar and base adenine, the nucleotide adenosine monophosphate (AMP) is formed; adding a second phosphoyrl group makes adenosine diphosphate (ADP); and adding a third makes ATP. Each compound can be made from the next smaller one plus a phosphate, H3PO4 (also known as inorganic phosphate) with the removal of water. This is an endergonic reaction and free energy is stored in ATP during the process. This energy is then retrieved when ATP is used to phosphorylate some other compound. When this happens the nucleotide loses a phosphate group, however there are some reactions in which both the terminal phosphates are removed together as pyrophosphate, H2P4O7. ATP is extremely important in cell metabolism. A large amount of energy is required in many cell reactions such as to couple together sugar residues to make a cellulose molecule or to ...

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