1.4.4Unit 1 — Cell Biology
Factors Affecting Enzyme Activity
5 min read 4 parts Lesson 19 of 28 Virtual lab
Section 1 of 4Temperature
1
At low temperatures enzyme and substrate molecules move slowly, so collisions are rare and the rate of reaction is low.
2
As the temperature rises the molecules gain kinetic energy, collide more often and the rate increases.
3
At the optimum temperature the enzyme works at its maximum rate; for human enzymes this is around 37 °C.
4
Above the optimum the enzyme's shape begins to change, the active site no longer fits and the rate falls rapidly.
5
At high temperatures the enzyme is denatured, which is permanent, so activity does not return on cooling.
Section 2 of 4pH
Optimum pH
- Each enzyme has a pH at which it works fastest, which suits the place it works in the body.
Pepsin
- Pepsin in the stomach works best in acid conditions, around pH 2.
Amylase
- Salivary amylase works best at about neutral pH, near 7.
Extreme pH
- Too acidic or too alkaline a pH changes the enzyme's shape and denatures it, so the rate falls.
Section 3 of 4Reading Graphs
Reading Graphs
Peak
- The highest point on the curve marks the optimum temperature or pH for that enzyme.
Rising section
- Before the peak, increasing temperature gives faster collisions and a faster reaction.
Falling section
- After the peak the rate falls because the active site shape is damaged.
Different enzymes
- Enzymes from different organisms or locations have different optima, such as enzymes in hot-spring bacteria.
Section 4 of 4Exam Checklist & Tips
1.4.4 – Key Points for the Exam
- Optimum The temperature or pH at which an enzyme works fastest.
- Denaturation A permanent change in an enzyme's shape that stops it working.
- Rate of reaction How quickly a reaction takes place, often measured as 1 divided by time.
- Kinetic energy The energy of movement of particles.
Common Mistakes
- Saying enzymes are killed by heat; they are denatured because they are not living.
- Writing that cooling a denatured enzyme restores it; the damage is permanent.
- Describing low temperature as denaturing; the enzyme is just slow and works again when warmed.
- Stating that all enzymes work best at 37 °C and pH 7.