Energetics in Biochemistry – ATP (10.1-10.3)
• Adenosine triphosphate (ATP) is used to generate energy to insure certain
biological processes proceed spontaneously
– 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)
– Whichever intermediate has the higher PTP is the better phosphate donor
Energetics in Biochemistry – Glycolysis (11.1-11.2)
• 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 conditions
– 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
• Formation of ATP occurs in two steps, where the PTP of the intermediates
is greater than that of ATP
– 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