A diagram of ATP labels its terminal phosphate linkage a "high-energy bond"

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Physical foundations of the living cell · Physical foundations of the living cell

Life at Thermal Energy, Ch Entropy, free energy and the forces that counting produces

Problem

A diagram of ATP labels its terminal phosphate linkage a "high-energy bond", suggesting that a fixed amount of energy is stored within that particular covalent bond and released whenever it is broken. In a certain cell type at body temperature (T=310 KT = 310\,\mathrm{K}, kBT=4.28 pN nmk_BT = 4.28\,\mathrm{pN\,nm}), the concentrations are [ATP]=5.0 mM[\mathrm{ATP}] = 5.0\,\mathrm{mM}, [ADP]=0.050 mM[\mathrm{ADP}] = 0.050\,\mathrm{mM} and [Pi]=2.0 mM[\mathrm{P_i}] = 2.0\,\mathrm{mM}. The standard free energy of hydrolysis is ΔG∘=−30.5 kJ mol−1\Delta G^{\circ} = -30.5\,\mathrm{kJ\,mol^{-1}} (standard state 1 M1\,\mathrm{M}, pH 7\mathrm{pH}\,7). ((a)) Calculate ΔG\Delta G for ATP hydrolysis under these cellular conditions, in kJ mol−1\mathrm{kJ\,mol^{-1}} and in kBTk_BT per molecule. ((b)) Explain, using your result, why it is misleading to say the bond itself stores this amount of energy.

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