Master
Enzymes.
Dive deep into Section 5 of the 697330-2026-2028-syllabus (2).pdf. Understand enzyme action, the lock and key hypothesis, and visually simulate the effects of temperature and pH on biological catalysts in real-time.
Open the menu on the left to access the Interactive Lab, Notes, and Examples.
Comprehensive Notes
5.1 Enzyme Action
- A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction.
- Enzymes are proteins that function as biological catalysts.
- Mechanism: The substance an enzyme acts upon is the substrate. It binds to the active site.
- When joined, they form an enzyme-substrate complex, which converts into products.
- Specificity: Explained by the 'lock and key' hypothesis. The active site has a complementary shape.
5.2 Effects of Temp & pH
- Temperature: As it increases to the optimum, molecules gain kinetic energy, increasing the frequency of effective collisions.
- Denaturation (Heat): Above optimum, strong vibrations break bonds. The active site shape is lost. The enzyme is denatured and substrate won't fit.
- pH: Extreme pH changes charges on amino acids, changing the 3D shape and leading to denaturation.
Interactive Lab: Real-time Kinetics
Adjust the sliders to see how temperature and pH affect the enzyme's active site and rate of reaction.
Environmental Controls
Temperature
37 °C
0°C (Low KE)
70°C (Denatures)
pH Level
7.0
Acidic
Alkaline
Reaction Rate
100%
Status
Optimum
Rate vs Temp
Molecular View
Denatured
Worked Examples (Mark Scheme Style)
Answer according to mark scheme:
- An enzyme is a protein that functions as a biological catalyst (1 mark).
- The substrate binds to the active site (1 mark).
Answer according to mark scheme:
- Explained by the 'lock and key' hypothesis (1 mark).
- The enzyme's active site has a specific, complementary shape (1 mark).
- That only fits a specific substrate, forming an enzyme-substrate complex (1 mark).
Ultimate Cheat Sheet
A* Exam Tips
- Say "frequency of effective collisions" when discussing temperature increases, not just "more collisions".
- Low temperatures do not denature enzymes. They just make them inactive due to low kinetic energy.
- Use the term denatured for both high heat and extreme pH damage. Never say "dies".