Q.26 During an enzyme catalyzed reaction, the equilibrium constant
(A) increases
(B) decreases
(C) remains unchanged
(D) can increase or decrease, depending on the enzyme

Answer: (C) remains unchanged

Enzymes act as catalysts that speed up biochemical reactions by lowering activation energy but do not alter the fundamental thermodynamics of the system. The equilibrium constant (K_eq), defined as the ratio of product to reactant concentrations at equilibrium, depends solely on temperature and the standard free energy change (ΔG°), not on the reaction pathway or catalyst presence. Since enzymes accelerate both forward and reverse reactions by the same factor, their ratio—and thus K_eq—stays constant.

Option Analysis

(A) Increases: Incorrect, as enzymes cannot shift equilibrium toward more products; they preserve the K_eq value determined by thermodynamics.

(B) Decreases: Incorrect for the same reason—K_eq reflects ΔG°, unaffected by catalytic rate enhancements.

(C) Remains unchanged: Correct, because enzymes multiply forward (k_f) and reverse (k_r) rate constants equally, keeping K_eq = k_f / k_r constant.

(D) Can increase or decrease, depending on the enzyme: Incorrect; no enzyme modifies thermodynamic equilibrium, regardless of type or specificity.

Introduction: Enzyme Catalyzed Reaction Equilibrium Constant Fundamentals
In enzyme catalyzed reactions, the equilibrium constant plays a pivotal role in understanding biochemical thermodynamics. This article delves into why the equilibrium constant remains unchanged during enzyme catalysis, analyzing all MCQ options with scientific evidence. Perfect for biotechnology students tackling questions on enzyme kinetics and equilibrium in competitive exams.

Thermodynamic Basis

The equilibrium constant K_eq = [Products]/[Reactants] at equilibrium derives from ΔG° = -RT ln K_eq, a temperature-dependent thermodynamic property. Enzymes lower activation energy (E_a) via transition state stabilization but leave ΔG° intact, ensuring no shift in equilibrium position.

• Catalysts speed attainment of equilibrium without altering final concentrations.

• Both forward and reverse rates increase proportionally (e.g., 100-fold enhancement keeps K_eq = k_f/k_r constant).​

• Applies universally to all enzymes, from proteases to kinases.

Common Misconceptions

Students often confuse rate constants (k) with equilibrium constants. Enzymes boost k_f and k_r equally per Arrhenius equation effects, but K_eq ratios persist. Visualized energy diagrams show lowered E_a barriers for both directions, converging at identical equilibrium.

Exam Relevance Table

This clarifies why option (C) prevails in questions like Q.26 for microbiology and biochemical engineering curricula.