Lesson overview
Enzymes: What temperature does an enzyme work best at?
Mix amylase with starch in a water bath and put a drop of the mixture onto iodine every 30 seconds until the starch has gone. Time it at six temperatures and three pH values, work out relative rates, and look inside the mixture at the active sites.
Suggested sequence
- Lesson 1 · Catalysts in living things. Catalysts and enzymes: the active site, the enzyme–substrate complex and why each enzyme has one job. Read together and discuss (15–20 min), practise with self-checking (20–25 min).
- Lesson 2 · Temperature and enzymes. Timing amylase at different temperatures: optimum temperature, collisions and denaturation. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 3 · pH and enzymes. Amylase at different pH values: buffers, optimum pH and the shape of the active site. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 9 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 7 questions, 15 min, lesson closed.
Learning goals
Part 1: Catalysts in living things
- Describe a catalyst as a substance that increases the rate of a chemical reaction and is not changed by the reaction (5.1.1)
- Describe enzymes as proteins that are involved in all metabolic reactions, where they function as biological catalysts (5.1.2)
- Describe why enzymes are important in all living organisms in terms of a reaction rate necessary to sustain life (5.1.3)
- Describe enzyme action with reference to the shape of the active site of an enzyme being complementary to its substrate and the formation of products (5.1.4)
- Explain enzyme action with reference to: active site, enzyme–substrate complex, substrate and product (5.1.6)
- Explain the specificity of enzymes in terms of the complementary shape and fit of the active site with the substrate (5.1.7)
Part 2: Temperature and enzymes
- Investigate and describe the effect of changes in temperature on enzyme activity with reference to optimum temperature and denaturation (5.1.5)
- Explain the effect of changes in temperature on enzyme activity in terms of kinetic energy, shape and fit, frequency of effective collisions and denaturation (5.1.8)
Part 3: pH and enzymes
- Investigate and describe the effect of changes in pH on enzyme activity, with reference to optimum and denaturation (5.1.5)
- Explain the effect of changes in pH on enzyme activity in terms of shape and fit and denaturation (5.1.9)
Misconceptions to listen for
- “A catalyst is used up as the reaction goes on.” — A catalyst is not changed by the reaction, so it can be used again.
- “A catalyst makes a reaction happen that could not happen at all.” — A catalyst speeds up a reaction that could already happen, only very slowly.
- “Enzymes are living things.” — Enzymes are protein molecules made by cells; they are not alive.
- “The active site is part of the substrate.” — The active site is a part of the enzyme; the substrate fits into it.
- “The enzyme changes into the products.” — The substrate changes into the products; the enzyme comes out unchanged.
- “Saliva contains as many amylase molecules as there are starch molecules.” — Only a little amylase is needed, because each molecule is used again and again.
- “Protein is too large for any enzyme.” — Proteases break down proteins; the point is that protein does not fit amylase’s active site.
- “Any enzyme that breaks down a sugar breaks down all sugars.” — Each enzyme is specific to the shape of its own substrate.
- “The body could just heat the blood to speed up clotting.” — Living things cannot heat their blood enough; enzymes make reactions fast at body temperature.
- “Only digestive enzymes are real enzymes.” — Every cell uses enzymes, for respiration, building molecules and much more.
Scope
Catalysts (5.1.1); enzymes as proteins and biological catalysts in all metabolic reactions (5.1.2); why life needs enzymes (5.1.3); the active site, substrate and products (5.1.4, Supplement 5.1.6 with the enzyme–substrate complex) and specificity (Supplement 5.1.7) in the reading and practice; the effect of temperature and pH on amylase with optimum and denaturation (5.1.5) through the starch–iodine practical, explained by kinetic energy, effective collisions, shape and fit (Supplement 5.1.8, 5.1.9). Times in the experiment come from a teaching model.