Summary
Coupled reactions and negative free energy changes determine pathway direction.
In depth
Reactions are linked: ΔG of coupled reactions add. Concentrations matter: actual ΔG differs from standard. Irreversible steps govern pathway direction. Cells maintain disequilibrium between ATP and ADP.
ΔG° differs from ΔG in cells. Metabolite concentrations pull reactions forward. Coupling to ATP hydrolysis makes unfavourable steps possible.
Key idea: reactions proceed in the direction of negative ΔG.
Metabolism obeys the laws of thermodynamics. The first law says energy is conserved; the second says that entropy of the universe increases, so living things maintain order by exporting heat and waste. Reactions with a negative change in Gibbs free energy (delta G) are spontaneous.
Delta G depends on concentrations: the real value in a cell differs from the standard value. Unfavourable reactions are driven forward by coupling to ATP hydrolysis (delta G about -50 kJ per mole in cells) or by being pulled by a subsequent favourable step. Enzymes lower activation energy but do not change delta G or equilibrium.
Example: glucose phosphorylation is coupled to ATP hydrolysis.
Common mistake: a reaction that is spontaneous may still be very slow without a catalyst.
Frequently asked questions
What is Thermodynamics of Metabolism?
Coupled reactions and negative free energy changes determine pathway direction.
Which area of biology covers Thermodynamics of Metabolism, and how advanced is it?
Thermodynamics of Metabolism is one of the 53 topics in Metabolism & Bioenergetics. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Metabolism, Oxidative Phosphorylation, Warburg Effect.
Can you give an example of Thermodynamics of Metabolism?
Hydrolysis of pyrophosphate pulls many biosynthetic reactions forward.
What should I learn before Thermodynamics of Metabolism?
Work through the Beginner topics in Metabolism & Bioenergetics first, such as Metabolism, Anabolism and Catabolism, ATP, then return to Thermodynamics of Metabolism. Advanced topics assume the Intermediate vocabulary.
What topics are related to Thermodynamics of Metabolism?
The closest topics to Thermodynamics of Metabolism are Metabolism, Oxidative Phosphorylation, Warburg Effect, ATP. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Thermodynamics of Metabolism?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Thermodynamics of Metabolism. To practise the whole of Metabolism & Bioenergetics, use the Metabolism & Bioenergetics quiz.
How is Thermodynamics of Metabolism different from Metabolism?
Thermodynamics of Metabolism: Coupled reactions and negative free energy changes determine pathway direction. Metabolism: The sum of all chemical reactions in an organism, including anabolic building and catabolic breakdown. Read both side by side and note what each one explains.
What is a common mistake about Thermodynamics of Metabolism?
A reaction that is spontaneous may still be very slow without a catalyst.
How should I study Thermodynamics of Metabolism step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Metabolism and explain the difference aloud. Finally, take the Metabolism & Bioenergetics quiz and come back to this page for any question you miss.