Interpreting Gibbs free energy (ΔG) in biochemistry If the change in Gibbs free energy (ΔG) for a chemical reaction has a negative value under cellular conditions, what does that indicate about the reaction’s energetics and spontaneity?

Introduction / Context:
Gibbs free energy (ΔG) predicts the direction and energy profile of biochemical reactions under defined conditions. Mastery of this concept is essential for understanding metabolism, coupling reactions, and how cells harness energy.

Given Data / Assumptions:

• ΔG refers to actual free energy change at cellular concentrations (not standard ΔG°′ unless specified).
• Negative ΔG indicates the products are lower in free energy than reactants.
• Temperature and pressure are constant (biological conditions).

Concept / Approach:
A negative ΔG denotes an exergonic reaction capable of proceeding spontaneously in the forward direction, often releasing energy that can appear as heat, be captured in ATP, or be used to drive endergonic steps via coupling. A positive ΔG indicates an endergonic, non-spontaneous process that requires energy input. ΔG = 0 indicates equilibrium.

Step-by-Step Solution:
Evaluate sign of ΔG: negative implies exergonic.Conclude that the reaction can proceed spontaneously toward products.Recognize that spontaneity does not guarantee high rate; enzymes control kinetics, not thermodynamics.

Verification / Alternative check:
Consider ATP hydrolysis with strongly negative ΔG under cellular conditions; it proceeds spontaneously and is exploited to drive biosynthetic reactions.

Why Other Options Are Wrong:

• Requires energy (endergonic) contradicts negative ΔG.
• Both (a) and (b): mutually exclusive.
• None of these: incorrect because (a) is correct.
• Equilibrium (ΔG = 0) does not apply when ΔG is negative.

Common Pitfalls:
Confusing ΔG with ΔG°′; actual intracellular concentrations can shift ΔG to negative even if ΔG°′ is positive, enabling pathways to proceed.

Final Answer:
It releases energy (exergonic) and can proceed spontaneously as written