GATE 2025 BT – Question 65

General Biology · Biochemistry: Metabolism of carbohydrates, lipids, amino acids and nucleic acids, glycolysis, citric acid cycle, fatty acid oxidation, photosynthesis, respiration and electron transport · 2 marks · Numerical answer

For the coupled reactions given below

Glucose 6-phosphate + H$_2$O $\rightarrow$ Glucose + P$_i$ (Reaction 1)

ATP + Glucose $\rightarrow$ ADP + Glucose 6-phosphate (Reaction 2)

the standard free energy change of ATP hydrolysis at 25 $^o$C is ____ kJ/mol. The equilibrium constants for Reaction 1 and Reaction 2 are 360 and 800, respectively; Gas constant R = 8.314 J mol$^{-1}$ K$^{-1}$. (Round off to two decimal places)

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Correct answer: -31.32 to -31.00

Explanation

Adding the two reactions gives ATP + H$_2$O $\rightarrow$ ADP + P$_i$, whose equilibrium constant is the product $K = 360 \times 800 = 2.88 \times 10^5$. So $\Delta G^o = -RT\ln K = -8.314 \times 298.15 \times 12.571 = -31160$ J/mol = $-31.16$ kJ/mol.