An Overview of Intermediary Metabolism and Bioenergetics - Biological Inorganic Chemistry - page 94

THE CENTRAL ROLE OF ATP IN METABOLISM
We can situate the importance of ATP in intermediary metabolism by some anecdotal information. The average ATP
molecule is hydrolysedwithinminutes of its synthesis (its turnover is very rapid). At rest, the average human consumes
around 40 kg of ATP per day, while during vigorous exercise, this may rise to around 0.5 kg/min! The hydrolysis of
ATP ( Figure 5.4 ) toADPandP i is accompanied by a relatively large free energy change 2 ( w 50 kJ/mole), as is that of

FIGURE 5.4 The chemical basis of the large free energy change associated with ATP hydrolysis. Hydrolysis is accompanied by relief of the
electrostatic repulsion between the negative charges on ATP by charge separation; the resulting phosphate anion is stabilised by resonance,
while the other product, ADP 2 þ releases a proton into a medium where [H þ ] is very low ( w 10 7 M).

ADP to AMP and P i . In contrast, the hydrolysis of AMP to adenosine and phosphate generates very little free energy
change. In biochemical terms, the importance of ATP as the energetic currency of the cell depends on the capacity of
the couple ATP/ADP to accept phosphoryl groups from high-energy donors and to donate phosphoryl groups to low
energy acceptors. Thus, to give an example from the glycolysis pathway described below, ATP can donate its

2. Where possible we have used the free energies D G calculated from in vivo concentrations of metabolites rather than the standard free
energies D G

, which do not take account of local concentrations of reactants and products.