Edexcel iGCSE Biology-2.11 temperature changes and enzyme function- Study Notes- New Syllabus

Effect of Temperature on Enzyme Function

📝 Introduction

Enzymes = proteins with an active site where the substrate fits.
Temperature changes can affect enzyme activity because they change the kinetic energy of molecules and the shape of the active site.

🔼 Low Temperature (Below Optimum)

• Molecules move slowly.
• Fewer collisions between enzyme + substrate.
• Reaction is very slow (but enzyme is not damaged).
• If temperature rises, rate increases.

🌟 Optimum Temperature

• Enzymes work best at a certain temperature (optimum).
• For human enzymes: ~37°C (body temp).
• At this point:
  • Max collisions between substrate + active site.
  • Fastest reaction rate.

🔥 High Temperature (Above Optimum)

• Enzyme molecules vibrate more strongly.
• Weak bonds holding the enzyme’s shape break.
• Active site changes shape = denatured.
• Substrate no longer fits → reaction stops.
• Denaturation is permanent.

📊 Temperature vs Enzyme Activity Curve

• Starts slowing at low temperatures.
• Steep rise as temperature increases → more collisions.
• Sharp peak at optimum.
• Sudden drop when enzyme denatures at high temperature.
• Graph is asymmetrical: rises gradually, falls sharply.

🧪 Example

• Human amylase: optimum ~37°C.
• Thermophilic bacteria enzymes: optimum ~70°C (used in hot springs and industrial reactions).

📊 Summary Table – Temperature Effects

⚡ Quick Recap
Cold → slow reaction, not damaged.
Optimum → maximum activity.
Too hot → denatured (active site shape changes, substrate no longer fits).
Graph = slow rise → peak → sudden drop.