60. The standard free energy change (ΔG°′) for ATP hydrolysis is
−30 kJ·mole−1. The in vivo concentrations of ATP, ADP and
Pi in E. coli are 7.90, 1.04 and 7.90 mM, respectively.
When E. coli cells are cultured at 37 °C, the free energy
change (ΔG) for ATP hydrolysis in vivo is
__________ kJ·mole−1.
Calculation Method
ATP hydrolysis follows ATP + H2O → ADP + Pi, with ΔG = ΔG°′ + RT ln Q, where Q = [ADP][Pi]/[ATP].
Concentrations convert to 0.00790 M ATP, 0.00104 M ADP, and 0.00790 M Pi, yielding Q = 0.00104.
At T = 310 K (37°C), R = 0.008314 kJ·mol-1·K-1, RT ln Q ≈ -17.7 kJ·mol-1, so ΔG = -30 + (-17.7) = -47.7 kJ·mol-1.
Biochemical Significance
In vivo, ΔG becomes more exergonic than ΔG°′ = -30 kJ·mol-1 because low Q (far below equilibrium K ≈ 105–106) drives energy release for cellular work.
E. coli maintains high ATP/ADP ratios via metabolism, enhancing ATP’s utility in biosynthesis and transport.
Common Options Explained
Typical multiple-choice options test formula application or unit errors:
| Option | Value (kJ·mol-1) | Reason Incorrect |
|---|---|---|
| -30.0 | Matches ΔG°′ | Ignores actual concentrations |
| -35.0 to -40.0 | Approximate errors | Wrong T (e.g., 298 K) or R |
| -47.7 | Correct | Uses 310 K, mM-to-M conversion |
| -50.0+ | Overestimation | Faulty ln Q or units |
This precise value underscores physiological thermodynamics in microbiology.
