Cellular reactions are held away from equilibrium by continual supply of substrates and removal of products.
Practise Kinetics & Equilibrium All Kinetics & Equilibrium topics
Living cells are not at chemical equilibrium, and their reactions are held away from equilibrium by a continuous supply of nutrients and continuous removal of waste products. Such open systems operate in a steady state, in which concentrations are constant because inflow and outflow balance, yet a net flux continues. Energy is supplied mainly through the hydrolysis of ATP and similar high energy compounds, which keeps the ratio of ATP to ADP and phosphate far from its equilibrium value. Reaching true equilibrium would mean that the gradients that drive biological work had disappeared, which corresponds to death.
Key ideas: Cells use coupling: an unfavourable reaction with delta G positive is driven by ATP hydrolysis with delta G about -30 to -50 kJ per mol under cell conditions, versus -30.5 kJ per mol standard. The actual delta G depends on Q: delta G = delta G standard + RT ln Q, and using biochemical standard state at pH 7 gives delta G0 prime. Metabolic pathways have a few irreversible regulated steps far from equilibrium.
Common mistakes and connections: Students believe that cellular reactions are all at equilibrium, or that a positive standard free energy blocks a reaction in a cell. Concentrations in cells make Q small enough that delta G becomes negative. Another mistake is mixing delta G0 prime with delta G standard at pH 0. Closely related to steady state versus equilibrium, Le Chatelier shifts by removal of products and to enzyme kinetics.
Cells keep gradients across membranes through continuous energy input; if they reached equilibrium the gradients driving biological work would vanish. The interactive lesson shows this as a live animation or chart.
In cells the ATP to ADP ratio is maintained far above the value that equilibrium with the surroundings would give.
Cellular reactions are held away from equilibrium by continual supply of substrates and removal of products.
Equilibrium in Biology is a advanced topic in Kinetics & Equilibrium. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in Kinetics & Equilibrium first: Surface Catalysis Steps, Zeolites, Reaction Coordinate Diagram.
The next topics in Kinetics & Equilibrium are Buffer Equilibria and Heterogeneous Equilibrium Vapor.
Yes. The interactive lesson includes a self-check question on Equilibrium in Biology, and the Kinetics & Equilibrium quiz draws on every topic in this area.
Equilibrium in Biology is topic 85 of 91 in Kinetics & Equilibrium.