Cambridge O Level Biology · Syllabus 5090 · Enzymes
Denaturation
What is Denaturation?
A permanent change in the three-dimensional shape of a protein caused by conditions such as temperature above the optimum or extreme pH, which disrupt the bonds holding the folded chain in place. When an enzyme is denatured its active site changes shape, the substrate is no longer complementary to it, fewer enzyme-substrate complexes form and activity falls.
This definition is part of the Enzymes chapter in Cambridge O Level Biology.
Denaturation in context
Enzymes are proteins that function as biological catalysts: each one increases the rate of a metabolic reaction and is not changed by that reaction, so a single enzyme molecule can catalyse the same reaction again and again. Cambridge O Level Biology (5090) Chapter 5 explains how an enzyme works through its active site, the enzyme-substrate complex and the lock-and-key model; why temperature and pH change the rate of an enzyme-catalysed reaction; what denaturation is and why it is not the same as being killed; and how to investigate amylase and catalase activity and interpret a product-time graph.
Common mistakes with Denaturation
- “The substrate is denatured at high temperature.” RepairThe enzyme is denatured. Denaturation is a change in the shape of a protein. WhyStarch, hydrogen peroxide and most other substrates are not proteins, so the word does not apply to them.
- “Above the optimum the molecules move too fast to fit into the active site.” RepairThe fall is caused by the active site changing shape through denaturation, not by speed. WhyFaster movement means more collisions, which would raise the rate. The only thing that can make it fall is losing working enzyme.