3.2.13 · Enzymes
Rate- Temperature — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 7 parts Lesson 9 of 17 Unit quiz
Lesson summary
3.2.1 Rate: Temperature — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how temperature changes the rate of an enzyme-catalysed reaction.Optimum — the temperature at which an enzyme catalyses a reaction at its maximum rate.Specific — each enzyme has its own …
- Slow molecules
- Fewer collisions
- Fewer complexes
- Low energy
- Faster molecules
- More collisions
Part 1 of 5Optimum temperature
Optimum
- Optimum the temperature at which an enzyme catalyses a reaction at its maximum rate.
Specific
- Specific each enzyme has its own optimum.
Part 2 of 5Low temperatures
Slow molecules
- Slow molecules enzymes and substrates move slowly.
Fewer collisions
- Fewer collisions fewer successful collisions occur between substrate and active site.
Fewer complexes
- Fewer complexes fewer enzyme–substrate complexes form.
Low energy
- Low energy collisions carry less energy, so bonds are less likely to be formed or broken.
Part 3 of 5Rising temperatures up to the optimum
Faster molecules
- Faster molecules molecules move faster.
More collisions
- More collisions successful collisions are more frequent.
More complexes
- More complexes more enzyme–substrate complexes form.
Higher energy
- Higher energy collisions are more likely to break or form bonds.
Part 4 of 5Temperatures above the optimum
Temperatures above the optimum
Denaturation
- Denaturation hydrogen bonds holding the enzyme in shape start to break.
Tertiary structure
- Tertiary structure it changes, permanently damaging the active site.
Binding fails
- Binding fails the substrate can no longer bind and the rate drops sharply.
Human enzymes
- Human enzymes few function above 50 °C because body temperature is about 37 °C.
Part 5 of 5More from the specification
More from the specification
Thermal enzyme rate determination
- Thermal enzyme rate determination measuring substrate consumption across varying incubation temperatures provides an empirical means to establish optimum activity.
Enzyme-Substrate Complex Formation
- Substrate molecules bind to complementary active sites on enzyme molecules,
- increasing reaction rate until active sites become saturated at maximum velocity (Vmax).
Competitive vs Non-Competitive Inhibition
- A competitive inhibitor competes with substrate for active sites,
- (raising Km without altering Vmax)
- whereas a non-competitive inhibitor binds allosteric sites, decreasing product formation and lowering Vmax.
Michaelis-Menten Constant (Km)
- The substrate concentration at which reaction rate reaches half of Vmax;
- a lower Km reflects higher enzyme-substrate affinity.
Industrial Immobilised Enzymes
- Enzymes entrapped within solid matrices such as alginate beads show increased resistance to thermal denaturation and can be easily recovered from product mixtures.
Buffer solution
- A solution that holds the pH at a fixed value.
Enzyme-substrate complex
- The temporary structure formed when a substrate binds to an enzyme's active site.
Inhibitor
- A molecule that reduces enzyme activity.
Lactose
- A disaccharide of glucose and galactose.
Affinity
- How readily haemoglobin binds oxygen.
Buffer
- A substance that resists pH change by absorbing or releasing H+.
Substrate concentration
- The amount of substrate per unit volume.
Enzyme concentration
- The amount of enzyme per unit volume.
Non-competitive inhibitor
- An inhibitor that binds elsewhere and changes the active site.
Immobilised enzyme
- An enzyme fixed to a surface or trapped in a matrix so it can be reused.
Key terms
| Term | Meaning |
|---|---|
| Optimum temperature | The temperature at which an enzyme works fastest. |
| Denaturation | Permanent change in shape of an enzyme's active site. |
| Kinetic energy | The energy of moving molecules. |
| Successful collision | A collision with enough energy and correct orientation. |
| Tertiary structure | The 3D folding of a polypeptide. |
| Hydrogen bond | A weak bond that holds protein shape. |
Avoid these mistakes
1
Saying enzymes die at high temperature — they are not alive; they denature.
2
Saying low temperature denatures enzymes — it only slows collisions.
3
Not explaining collision frequency — link temperature to the number of successful collisions.
4
Saying denaturation is reversible — it is usually permanent.
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