Concept preview

What you will be able to do

1. 01Describe and explain how temperature affects enzyme rate up to an optimum and beyond.
2. 02Explain what denaturation is and why it is usually irreversible.
3. 03Describe how pH affects rate and why enzymes such as pepsin and trypsin have different optima.
4. 04Explain the effect of substrate concentration, saturation and Vmax, and of enzyme concentration.
5. 05Read and interpret enzyme rate graphs correctly.

An enzyme's power comes entirely from its precise three-dimensional shape — the shape that builds its active site. Anything in the surroundings that changes how fast substrate and enzyme meet, or that alters that delicate shape, will change how quickly the enzyme works. In this topic we examine the four factors that matter most: temperature, pH, substrate concentration and enzyme concentration. Understanding them is not merely academic. It is why food is kept in a refrigerator, why your stomach is acidic, why a high fever is dangerous, and how biological washing powders lift stains. In each case the key is to ask a single question: is this factor changing how often the enzyme and substrate collide, or is it changing the shape of the active site itself? Keeping those two ideas separate is the secret to interpreting every graph in this topic correctly, because they produce very different curves.