Explain how heating the enzyme amylase to 80 °C denatures it and affects its catalytic activity. In your answer, describe (i) the type of structural changes that occur in the protein, (ii) the effect on the geometry of the active site, and (iii) the resulting change in the rate of starch hydrolysis, providing a brief mechanistic rationale.

Step-by-step solution

1. Identify the level of protein structure affected by heating: high temperature breaks weak non‑covalent forces (hydrogen bonds, hydrophobic interactions, ionic bonds) that stabilise the tertiary structure.
2. Explain that the primary peptide backbone remains intact, but the overall three‑dimensional folding is lost, leading to an unfolded or misfolded protein.
3. Describe the active site: it is formed by residues that are brought together in the correctly folded tertiary structure.
4. When the tertiary structure is disturbed, the precise orientation of these residues changes; the catalytic pocket may become wider, narrower, or completely lost.
5. Because substrate binding depends on the exact shape and charge distribution of the active site, the altered geometry reduces the enzyme’s affinity for starch and hampers transition‑state stabilisation.
6. According to the Michaelis‑Menten model, a decrease in effective enzyme concentration (or increase in Kₘ) leads to a lower initial reaction rate (V₀).
7. Thus, heating amylase to 80 °C causes denaturation, destroys the active‑site architecture, and the rate of starch hydrolysis drops dramatically, often to near‑zero.

Concept tested: Protein denaturation and enzyme activity

Published 5 September 2026 · How this solution was prepared and checked