Biochemistry: Coupled Reactions

Coupled Reactions

• Coupled reactions combine a spontaneous exergonic reaction with a non-spontaneous endergonic reaction, enabling the latter to proceed through energy transfer.

Example of a Coupled Reaction

• The hydrolysis of ATP, an exergonic process, can be coupled with the endergonic reaction of glucose converting into lactic acid, maintaining a negative change in Gibbs free energy (ΔG).

ΔG and Work

• ΔG represents the maximum amount of work obtainable from a chemical reaction, providing insights into the efficiency and spontaneity of the reaction.

ΔG as Driving Force

• Change in Gibbs free energy (ΔG) serves as the driving force behind both physical and chemical transformations, indicating whether a process can occur spontaneously.

Equilibrium Condition

• When ΔG equals zero, the system is in a state of equilibrium, meaning there is no net change occurring in the concentration of reactants and products.

Equations for ΔG

• Two key formulas for calculating ΔG include:
  • ΔG = ΔG° + RT ln Q
  • ΔG = -RT ln K
• These equations relate standard Gibbs free energy change to reaction quotients (Q) and equilibrium constants (K).