Summary
Reactions proceed spontaneously when the change in Gibbs free energy is negative; ATP hydrolysis drives unfavourable ones.
In depth
Gibbs free energy change equals ΔH minus TΔS. Negative ΔG reactions are exergonic and can proceed; positive ones are endergonic. Coupling links an unfavourable reaction to ATP hydrolysis (about -30.5 kJ per mole under standard conditions, more in cells).
Equilibrium has ΔG zero, and living cells are kept far from equilibrium by continuous input of energy.
Key idea: life maintains order locally by increasing entropy elsewhere.
ΔG depends on conditions, not only standard values, and cells keep reactions away from equilibrium by removing products, so reactions in pathways run in a forward direction. Standard values for ATP hydrolysis are about minus 30.5 kJ per mole, but inside cells it can reach minus 50 or more because the ATP to ADP ratio is far from equilibrium.
Enthalpy changes reflect bond energy; entropy changes reflect disorder. Living things stay ordered by exporting entropy as heat and waste, which does not violate the second law, since the universe as a whole becomes more disordered.
Frequently asked questions
What is Free Energy in Biology?
Reactions proceed spontaneously when the change in Gibbs free energy is negative; ATP hydrolysis drives unfavourable ones.
Which area of biology covers Free Energy in Biology, and how advanced is it?
Free Energy in Biology is one of the 51 topics in Biomolecules & Biochemistry. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include pH and Buffers, Protein Folding and Chaperones, Activation Energy.
Can you give an example of Free Energy in Biology?
Protein folding is driven mainly by the entropy gain in the surrounding water when hydrophobic parts are buried.
What should I learn before Free Energy in Biology?
Work through the Beginner topics in Biomolecules & Biochemistry first, such as Water Properties, Carbon Chemistry, Carbohydrates, then return to Free Energy in Biology. Advanced topics assume the Intermediate vocabulary.
What topics are related to Free Energy in Biology?
The closest topics to Free Energy in Biology are pH and Buffers, Protein Folding and Chaperones, Activation Energy, Water Properties. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Free Energy in Biology?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Free Energy in Biology. To practise the whole of Biomolecules & Biochemistry, use the Biomolecules & Biochemistry quiz.
How is Free Energy in Biology different from pH and Buffers?
Free Energy in Biology: Reactions proceed spontaneously when the change in Gibbs free energy is negative; ATP hydrolysis drives unfavourable ones. pH and Buffers: The pH scale measures hydrogen ion concentration; buffers resist pH change to keep conditions stable in cells. Read both side by side and note what each one explains.
How should I study Free Energy in Biology 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 pH and Buffers and explain the difference aloud. Finally, take the Biomolecules & Biochemistry quiz and come back to this page for any question you miss.