Energetics in Biochemistry – ATP ( ) Adenosine triphosphate (ATP) is used to generate energy to insure certain biological processes proceed spontaneouslyATP – Hydrolysis of ATP to form adenosine diphosphate (ADP) is exergonic (energy is released) by about 30 kJ/mol in the biochemical standard state – ATP is reformed from ADP through phosphorylation (during glycolysis) Many biochemical processes are coupled to the hydrolysis of ATP because by themselves they are endergonic (energy must be absorbed) – Phosphorylated intermediates are generated when ATP is used – Principle of common intermediates requires the intermediate to be utilized in one of the following steps (essentially just Hess’s law) Since phosphorylated species are generated and hydrolyzed in these ATP/ADP coupled reactions, it is important to know which species are the most effective phosphate donors – Phosphate transfer potentials are used to determine which species are the most effective phosphate donors (value is negative of Gibbs energy of hydrolysis) Phosphate transfer potentials – Whichever intermediate has the higher PTP is the better phosphate donor

Energetics in Biochemistry – Glycolysis ( ) Glycolysis is the process of breaking down glucose to form 2 pyruvate molecules – Pyruvate is used in the Krebs cycle to form reducing agents (e.g., NADH) used in the electron transport chain – Some ATP is also synthesized during glycolysis Formation of some intermediates in the glycolytic pathway are endergonic under standard biochemical conditionsglycolytic pathway – ATP hydrolysis can be used to make formation of these intermediates exergonic (e.g., phosphorylation of glucose – step 1) – Cellular conditions are not standard, so the actual Gibbs energy changes are exergonic (or nearly exergonic) under these conditions Cellular conditions Formation of ATP occurs in two steps, where the PTP of the intermediates is greater than that of ATPPTP – Steps that form ATP require energy to be put into the synthesis of ATP from ADP

ATP

Phosphate Transfer Potentials

Glycolysis – Steps 1-5

Glycolysis – Steps 6-10

Glycolysis Under Standard and Cellular Conditions

PTP of Glycolytic Intermediates