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ATP and energy coupling – ATP hydrolysis drives endergonic reactions, the ATP–ADP cycle

BiologyCell BiologyAges 15–16

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Three screens on ATP as the cell's energy currency. ΔG bars show ATP hydrolysis (ATP + H₂O → ADP + Pi, ΔG°′ ≈ −30.5 kJ/mol) coupled to glutamine synthesis, the Na⁺/K⁺ pump or muscle contraction so that the total ΔG is negative. The ATP–ADP cycle shows ATP remade by respiration or photosynthesis as energy demand changes, and a chemistry example of coupling (reducing a metal oxide with carbon) gives ΔG = ΔH − TΔS for each step at any temperature.

Lesson: ATP and energy coupling: hydrolysis and synthesis of ATP, coupled reactions, Gibbs free energy

What it shows

This simulation shows how cells use ATP to drive reactions that would not happen on their own, for ages 15–18. Students compare the ΔG of glutamine synthesis, the sodium-potassium pump and a myosin power stroke with the ΔG of ATP hydrolysis, under standard or cell conditions, and see in a waterfall chart when the coupled total is negative. They then follow the ATP–ADP cycle as respiration or photosynthesis remakes ATP for a changing demand, and compare a chemical example, reducing metal oxides with carbon, using ΔG = ΔH − TΔS. Values are textbook data with simplified models.

How to use

On Energy coupling, choose the Energy-requiring process and the Conditions for ATP's ΔG, untick Coupled to ATP hydrolysis to compare, and move the Load force for muscle. On ATP–ADP cycle, choose the Source for remaking ATP and move Energy demand. On Coupling in chemistry, choose the Reaction and move the Temperature.

Parameters you can change

  • Starting screen Energy coupling, ATP–ADP cycle, Coupling in chemistry
  • Energy-requiring process Glutamine synthesis, Na⁺/K⁺ pump (active transport), Muscle contraction (myosin pulling actin)
  • Conditions for ATP's ΔG Standard (ΔG°′ = −30.5 kJ/mol), In a cell (typical concentrations)
  • Coupled to ATP hydrolysis
  • Load force on one myosin head 0–10 pN
  • Source for remaking ATP Aerobic respiration, Anaerobic respiration (lactate), Photosynthesis (light-dependent reactions)
  • Energy demand 0–100 %
  • Light intensity 0–100 %
  • Metal oxide reduction Iron(III) oxide + carbon, Zinc oxide + carbon, Copper(II) oxide + carbon
  • Temperature 298–2000 K

Questions to explore

  1. Why can a reaction with a positive ΔG happen in a cell when it is coupled to ATP hydrolysis?
  2. Why does the sodium-potassium pump work in a cell but not with the standard ΔG°′ of ATP?
  3. Above what temperature does carbon reduce iron(III) oxide in this model, and why?

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