The Gibbs Function and Useful Work in Biologic Systems

As biologic systems operate at constant temperature and pressure, the change in the Gibbs function of a reaction occurring in a biologic system is a measure of the maximum magnimde of the net useful work that can be obtained from the reaction. 

The hydrolysis of adenosine triphosphate (ATP), an exergonic reaction [Equation (7.89)], is frequently used in biologic systems to drive endergonic reactions. The value of AGmfor this reaction is —29,3001 mol  

For ATP to carry out this function, it has to be produced from adenosine diphosphate (ADP) in an endergonic reaction that must be driven by another exergonic metabolic reaction. One exergonic reaction step that occurs in the overall oxidation of glucose in the cell is the oxidation of 3-phosphoglyceraldehyde to 3-phosphoglycerate by pyruvate, for which AG = —29,300 Jmol  

As it occurs in the cell, the reaction (Equation 7.90) involves a mole of inorganic phosphate  

3-diphosphoglycerate that is formed then reacts with adenosine diphosphate to form adenosine triphosphate and 3-phosphoglycerate  

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