Enzyme Activity Lab

Enzymes are biological catalysts — proteins that speed up reactions by factors of millions without being consumed. Nearly every chemical process in your body depends on one. But they are fussy: their performance swings wildly with conditions.

Temperature: a trade-off

Raising temperature does two opposing things at once:

• It gives molecules more kinetic energy, so they collide more often and more forcefully — the reaction speeds up.
• It starts to shake the enzyme’s folded structure apart — the reaction collapses.

The result is a sharp peak. Human enzymes typically peak near 37 °C. A few degrees above that, the delicate hydrogen bonds holding the protein’s shape give way and the active site loses its form. This is denaturation, and it is largely irreversible — it is why a high fever is dangerous and why cooking destroys the enzymes in food.

pH: charge matters

Each enzyme has an optimum pH where its active site has exactly the right pattern of electrical charges to bind its substrate. Move away from that and the charges change, binding weakens, activity falls. Pepsin in the stomach works at pH 2; trypsin in the small intestine prefers pH 8.

Michaelis–Menten kinetics

At fixed temperature and pH, rate depends on substrate concentration:

v = Vmax · [S] / (Km + [S])

• Vmax — the ceiling, when every enzyme molecule is busy.
• Km — the substrate concentration at half Vmax. Low Km means the enzyme binds tightly and reaches half speed with little substrate.

Try this

• Push temperature past 45 °C and watch the rate crash even though molecules are moving faster than ever.
• Shift pH a couple of units from the optimum — activity drops without any permanent damage.
• Add substrate steadily and watch the curve flatten as the enzymes saturate.

Why it matters

Enzyme kinetics drives drug design (most drugs work by blocking an enzyme), industrial biotechnology (detergent enzymes that work cold), food science, and the interpretation of medical blood tests that measure enzyme levels as damage markers.