Enzymes

Enzymes as catalysts

• An enzyme is a biological catalyst: a substance that speeds up chemical reactions.
• A higher enzyme concentration gives a faster rate: more active sites, so more enzyme-substrate complexes form.

How an enzyme works

1. The substrate fits into the active site of the enzyme.
2. The active site is complementary to the substrate.
3. The substrate binds to the active site and an enzyme-substrate complex forms.
4. The substrate reacts and the products are released.

Temperature

Rising to the optimum

1. Increasing temperature gives the enzyme and substrate molecules more kinetic energy.
2. They collide more frequently.
3. More enzyme-substrate complexes form.
4. Activity is greatest at the optimum temperature.

Above the optimum

1. The active site changes shape.
2. The enzyme is denatured.
3. The substrate no longer fits the active site.

• At a low temperature the molecules have less kinetic energy and collide less often; the enzyme is not denatured.
• Write enzymes denature. Never write the yeast denatures.

pH

1. Each enzyme works best at its optimum pH.
2. Away from the optimum pH the active site shape changes and the enzyme denatures.
3. The substrate no longer binds to the active site.

Write enzymes denature in acid. Never write that enzymes denature due to high temperature when the cause is pH.

Investigating temperature

An indicator shows the end point of the reaction, from the change in pH.