LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- define catalyst and enzyme
- explain enzyme specificity
- describe enzyme-substrate complexes
- interpret effects of temperature and pH
THE BIG IDEA
Why biological reactions need specific catalysts and how conditions alter their activity.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
SECTION 01
Enzyme action
Enzymes are proteins that act as biological catalysts. Their active site has a three-dimensional shape complementary to a particular substrate.
DETAILED EXPLANATION
- The substrate binds to form an enzyme-substrate complex.
- The reaction produces products, which leave; the unchanged enzyme can be reused.
- Specificity arises because only suitable substrates fit the active site.
- Enzymes make metabolic reactions fast enough to sustain life.
SECTION 02
Temperature
At low temperature, molecules have less kinetic energy and fewer collisions are successful. Warming increases collision frequency until the optimum is reached.
DETAILED EXPLANATION
- Above the optimum, bonds maintaining enzyme shape break.
- The active site changes so the substrate no longer fits; this is denaturation.
- Cooling slows an enzyme but usually does not permanently alter its shape.
SECTION 03
pH and investigation
Each enzyme has an optimum pH. Conditions far from it alter bonds and active-site shape, reducing successful binding and possibly denaturing the enzyme.
DETAILED EXPLANATION
- Change one independent variable while controlling enzyme and substrate concentration, volume and other conditions.
- Measure rate using product formed per unit time or time for substrate disappearance.
- Repeat readings and calculate a mean.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Enzymes are reusable protein catalysts.
- Complementary shape explains specificity.
- Temperature affects collisions and structure.
- Extreme temperature or pH can denature an enzyme.