Biochemistry — Enzymes: Which one of the following statements is NOT true? (Consider general enzyme properties applicable in biochemistry and biotechnology.)

Introduction:
Enzymes are biological catalysts that increase reaction rates without being consumed. This question tests core concepts about what enzymes can and cannot do, their chemical nature, and where they function.

Given Data / Assumptions:

• General properties of enzymes are being compared.
• No organism- or pathway-specific exceptions are required.
• Terms such as activation energy and thermodynamic favorability are used in their standard biochemical sense.

Concept / Approach:
Evaluate each statement against accepted biochemical principles: enzyme composition (protein vs RNA), catalytic mechanism (lowering activation energy), thermodynamics (no change in ΔG), and operational context (in vivo vs in vitro activity).

Step-by-Step Solution:
1) Enzymes as proteins: Correct. While ribozymes exist, most enzymes are proteins that bind substrates specifically and accelerate reactions.2) Activation energy: Correct. Catalysis proceeds by lowering the activation energy (Ea), increasing the fraction of molecules reaching the transition state.3) Thermodynamics: Correct. Enzymes do not change ΔG or the position of equilibrium; they only change the rate of reaching equilibrium. They cannot make an unfavorable (positive ΔG) reaction proceed unless coupled to a favorable one.4) Function only in intact cells: Incorrect. Many enzymes are active in vitro and in industrial, clinical, and lab settings outside cells.

Verification / Alternative check:
Examples include DNA polymerases, proteases (trypsin), and restriction endonucleases used routinely outside cells, confirming statement (d) is false.

Why Other Options Are Wrong:

• (a) True: captures specificity and rate enhancement.
• (b) True: mechanism centers on lowering Ea.
• (c) True: kinetics change; thermodynamics do not.
• (e) True: acknowledges ribozymes while noting most catalysts are proteins.

Common Pitfalls:
Confusing “overcoming” with “lowering” activation energy; thinking enzymes shift equilibrium; assuming enzymes are only active in vivo.

Final Answer:
Enzymes only function when they are inside intact, living cells and are inactive outside cells.