In an engineered metabolic pathway, the phosphorylation of a hexose sugar has a standard free energy change of ΔG∘=+13.8 kJ/mol. When this reaction is coupled to ATP hydrolysis (ΔG∘=−30.5 kJ/mol), the overall process proceeds spontaneously. A student proposes that increasing the concentration of the kinase enzyme or introducing an inorganic catalyst could make the uncoupled sugar phosphorylation spontaneous without ATP. Which statement correctly evaluates this proposal based on thermodynamic principles?
- A) The proposal is incorrect because enzymes and catalysts only lower the activation energy barrier without altering the free energy of reactants or products, meaning they cannot convert an endergonic reaction into an exergonic one.
- B) The proposal is correct because a sufficiently high enzyme concentration alters the equilibrium constant by lowering the standard free energy level of the products below that of the reactants.
- C) The proposal is incorrect because catalysts accelerate only the reverse direction of reactions with positive free energy changes, shifting the equilibrium toward substrate accumulation.
- D) The proposal is correct because inorganic catalysts supply enthalpy directly to reactants, permanently converting a positive Gibbs free energy change into a negative one.
