Energy coupling Transitional Reasoning Practice

Questions

1. 1.

   In cellular metabolism, the conversion of glutamic acid to glutamine is an endergonic process with a standard free-energy change of $\Delta G = +14.2\text{ kJ/mol}$. To make this vital synthesis spontaneous, the cell couples it to the exergonic hydrolysis of ATP ($\Delta G = -30.5\text{ kJ/mol}$) via a two-step enzymatic reaction. Based on the principles of energy coupling, which statement best explains how ATP hydrolysis drives this non-spontaneous reaction forward?

   • A) The transfer of a phosphate group from ATP to glutamic acid forms a reactive intermediate whose subsequent reaction with ammonia yields a net negative free-energy change.
   • B) The rapid release of thermal energy from ATP hydrolysis warms the enzyme active site to turn an endergonic conversion into an exergonic one.
   • C) Hydrolysis of ATP increases the total activation energy of the pathway so that glutamic acid converts into glutamine without enzyme assistance.
   • D) The inorganic phosphate cleaved from ATP permanently binds to the glutamine molecule to stabilize its structure as a final metabolic product.

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