Regarding the free energy change of a biochemical reaction, which statement is correct?

• A Delta G0 prime determines whether a given amount of reaction will proceed under actual cellular conditions
• B A reaction with a positive delta G0 prime can never proceed forward inside a cell
• C At equilibrium, delta G reaches its most negative value
• D Delta G of a reaction depends on the concentrations of reactants and products in the cell ✓

Explanation

Delta G is the actual free energy change and varies with the mass action ratio of products to reactants, so it reflects real cellular conditions. Delta G0 prime is fixed for a reaction at standard conditions and cannot alone predict direction in vivo. At equilibrium delta G equals exactly zero, not a minimum negative value, and no net reaction occurs. Many biosynthetic pathways drive positive delta G0 prime steps forward by coupling them to ATP hydrolysis or by keeping product concentrations low.

Reference: Lehninger Principles of Biochemistry (Nelson and Cox), 7th ed.

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