Temperature and pH
Temperature and pH
- Enzyme activity depends on temperature and pH.
- Both have an optimum — a best value.
- Too far from it, the enzyme is denatured.
Temperature
- As temperature rises from cold, activity speeds up (more kinetic energy, more collisions).
- Activity peaks at the optimum (about 37 °C in humans).
- Above the optimum, the heat changes the shape of the active site → the substrate no longer fits → the enzyme is denatured (permanent).
Practice
As temperature rises above the optimum, enzyme activity:
Above the optimum, heat changes the active site shape (denaturation), so activity drops sharply.
Practice
When an enzyme is denatured:
Denaturation changes the active site shape permanently; the substrate can no longer fit.
pH
- Each enzyme works best at one optimum pH.
- Too high or too low a pH also changes the active site shape and denatures the enzyme.
Practice
Each enzyme works best at:
Far from its optimum pH, the active site changes shape and the enzyme is denatured.
You've got it
Key idea
- activity rises to the optimum temperature (~37 °C), then falls as the enzyme denatures
- denatured = the active site shape changes so the substrate no longer fits (permanent)
- each enzyme has an optimum pH; far from it, it is denatured
- "denatured" does not mean "killed" — enzymes are not alive
Practice
Saying an enzyme is "killed" is wrong — enzymes are not alive.
Enzymes are molecules, not living things; the correct word is "denatured".