CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
In cellular metabolism, glucose can be phosphorylated by inorganic phosphate (Pᵢ) in a reaction that, by itself, is thermodynamically unfavorable:
Glucose + Pᵢ → Glucose-6-phosphate + H₂O ΔG°₁ = +13.8 kJ mol⁻¹
The reaction is driven forward in vivo by coupling it to the hydrolysis of adenosine triphosphate (ATP):
ATP + H₂O → ADP + Pᵢ ΔG°₂ = –30.5 kJ mol⁻¹
(a) Write the overall chemical equation obtained when the two reactions above are coupled through their common intermediate Pᵢ.
(b) Calculate the net ΔG° for the coupled process.
(c) Explain, with reference to free-energy concepts, why the coupled process proceeds spontaneously whereas the phosphorylation of glucose alone does not.
(d) Describe the role of the common intermediate in ensuring that energy released from ATP hydrolysis is effectively transferred to drive glucose phosphorylation.