Endergonic

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Endergonic

Description

Endergonic transformations or processes can proceed in the forward direction only by coupling to an exergonic process with a driving force more negative than the positive force of the endergonic process. The backward direction of an endergonic process is exergonic. The distinction between endergonic and endothermic processes is at the heart of ergodynamics, emphasising the concept of exergy changes, linked to the performance of work, in contrast to enthalpy changes, linked to heat or thermal processes, the latter expression being terminologically linked to thermodynamics.


Reference: Gnaiger 1993 Pure Appl Chem

Communicated by Gnaiger E 2018-12-29

Examples

  • ATP synthase: Phosphorylation of ADP to ATP is an endergonic reaction in an over-all exergonic process that is driven by proton translocation along the protonmotive force, ∆mFH+. Then ∆mFH+ is seen in the exergonic direction of proton flux from the external (positive) to the matrix space (negative).
  • Coupled OXPHOS: When discussing electron transfer coupled to the generation of ∆mFH+, then the exergonic process is electron transfer, and ∆mFH+ is defined in the endergonic direction of protons translocated from the matrix space (negative) to the external space (positive).


Discussion

Different definitions of the terms exergonic and endergonic derive from the thermodynamics of irreversible processes [1] versus classical thermodynamics with an emphasis on standard Gibbs energy changes [2], in contrast to Gibbs energy changes estimated for actual states.


IUPAC definition

Endergonic (endoergic) reaction: This is usually taken to be a reaction for which the overall standard Gibbs energy change ΔG° is positive. Some workers use this term with reference to a positive value of ΔH° at the absolute zero of temperature [2].


References

  1. Gnaiger E (1993) Nonequilibrium thermodynamics of energy transformations. Pure Appl Chem 65:1983-2002. - »Bioblast link«
  2. IUPAC (1997) Compendium of chemical terminology, 2nd ed (the "Gold Book"). Compiled by McNaught AD, Wilkinson A. Blackwell Scientific Publications, Oxford. XML on-line corrected version: http://goldbook.iupac.org (2006-) created by Nic M, Jirat J, Kosata B; updates compiled by Jenkins A. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook. Last update: 2014-02-24; version: 2.3.3.


MitoPedia concepts: Ergodynamics