Q91. Enzymes catalyze biochemical reactions by
- Sequestering the product(s)
- Decreasing the ΔG of the reaction
- Increasing the ΔG of the reaction
- Stabilizing the transition state of the reaction
Enzymes accelerate reactions by lowering activation energy without altering equilibrium or net free energy change (ΔG). They bind substrates specifically and facilitate bond breaking/forming through precise active site geometry. This enables life-sustaining metabolism under mild physiological conditions.
Correct Answer
Enzymes catalyze biochemical reactions by stabilizing the transition state of the reaction.
The transition state represents the highest energy intermediate where bonds partially form/break; enzyme binding preferentially stabilizes this fleeting structure, reducing activation energy (Eₐ).
Rate acceleration (often >10⁶-fold) occurs as enzymes bind transition states 10²⁻10⁴ times tighter than substrates.Option Analysis
Sequestering the Product(s)
Product binding would inhibit catalysis by preventing substrate access (product inhibition).
Enzymes release products rapidly post-reaction to maintain turnover.
Opposite of catalytic mechanism.Decreasing the ΔG of the Reaction
ΔG determines reaction spontaneity and equilibrium; enzymes cannot change thermodynamics, only kinetics.
They lower Eₐ (transition state energy), not overall ΔG.
Incorrect; violates fundamental bioenergetics.Increasing the ΔG of the Reaction
Higher ΔG would make reactions less favorable, slowing them further.
Enzymes accelerate both directions equally near equilibrium.
Mechanistically impossible.Stabilizing Transition State (Correct)
Active site residues form electrostatic interactions, H-bonds, or covalent intermediates with transition state geometry.
Examples: serine proteases stabilize oxyanion hole; lysozyme binds distorted sugar ring.
Core principle of transition state theory in biocatalysis.Option Correct Mechanism? Effect on Reaction Key Principle Sequestering products No Inhibits turnover Product inhibition Decreasing ΔG No Changes thermodynamics Enzymes kinetic catalysts Increasing ΔG No Slows reaction Violates catalysis Stabilizing transition state Yes Lowers Eₐ Transition state theory This mechanism underlies enzyme specificity, drug design (transition state analogs), and metabolic efficiency.
