Enzyme denaturation is usually observed at which temperature range?

• A. 40–50 C
• B. 60–65 C
• C. 20–30 C
• D. 70–80 C

Answer: (A)

Proteins, including enzymes, rely on noncovalent interactions that hold their folded structure together. When heat is applied, those interactions weaken and break, causing the molecule to unwind and lose its precise active-site shape. This loss of structure is denaturation, accompanied by a sharp drop or complete loss of catalytic activity.

For many standard enzymes, the onset of denaturation begins around 40–50°C. Below this range, the enzyme remains folded and active, though reaction rates may change with temperature. At higher temperatures such as 60–65°C or 70–80°C, denaturation becomes more rapid and extensive, often resulting in irreversible inactivation. (Note that some thermophilic enzymes tolerate higher temperatures, but in typical teaching examples, 40–50°C is the common range where denaturation starts to appear.)