Factors that affect enzyme activity
Cambridge A-Level Biology (9700) · Unit 3: Enzymes · 9 flashcards
Factors that affect enzyme activity is topic 3.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 3 — Enzymes , alongside Mode of action of enzymes. In one line: Vmax (maximum velocity) is the maximum rate of reaction achieved by an enzyme when it is saturated with substrate. It represents the point where increasing substrate concentration no longer increases the reaction rate because all enzyme active sites are occupied.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 9 flashcards — 2 definitions and 7 key concepts — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Vmax in the context of enzyme kinetics
Vmax (maximum velocity) is the maximum rate of reaction achieved by an enzyme when it is saturated with substrate. It represents the point where increasing substrate concentration no longer increases the reaction rate because all enzyme active sites are occupied.
What the Cambridge 9700 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Investigate and explain how the rate of an enzyme-catalysed reaction is affected by temperature, by pH (set with buffer solutions) and by the concentrations of enzyme, substrate and inhibitor.
- Explain that the Michaelis-Menten constant (Kₘ) is derived from Vₘₐₓ, the highest reaction rate, and that Kₘ lets you compare how much affinity different enzymes have for their substrates.
- Explain how enzyme activity is affected by reversible inhibitors of both kinds, competitive and non-competitive.
- Investigate how an enzyme's activity compares when it is free in solution and when it is immobilised in alginate, and state what advantages immobilised enzymes offer.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Factors that affect enzyme activity
- › Explain that the rate levels off because the enzyme active sites are 'saturated' with substrate, making the enzyme concentration the limiting factor.
- › Analyze enzyme graphs carefully to identify where the reaction rate levels off or where substrate availability becomes the limiting factor.
- › Use technical terms like 'reaching Vmax' or 'maximum rate of activity' to describe the upper limit of an enzyme-controlled reaction.
- › Note that with competitive inhibitors, increasing the substrate concentration can overcome inhibition to reach the same Vmax as an uninhibited reaction.
- › In the exam, draw lines on your graph to show exactly where you read the values for Vmax and 1/2 Vmax.
How does increasing temperature generally affect the rate of an enzyme-catalyzed reaction?
Generally, increasing temperature increases the rate of reaction because more molecules have sufficient kinetic energy to overcome the activation energy. However, beyond the optimum temperature, the enzyme denatures, and the rate decreases rapidly.
Explain the effect of pH on enzyme activity.
Enzymes have an optimum pH at which they function most effectively. Deviations from this pH can disrupt the ionic and hydrogen bonds that maintain the enzyme's tertiary structure, leading to denaturation and reduced activity.
Define Vmax in the context of enzyme kinetics.
Vmax (maximum velocity) is the maximum rate of reaction achieved by an enzyme when it is saturated with substrate. It represents the point where increasing substrate concentration no longer increases the reaction rate because all enzyme active sites are occupied.
What is the Michaelis-Menten constant (Km) and what does it indicate?
The Michaelis-Menten constant (Km) is the substrate concentration at which the reaction rate is half of Vmax. Km is a measure of the affinity of an enzyme for its substrate; a lower Km indicates a higher affinity.
Describe how a competitive inhibitor affects enzyme activity.
A competitive inhibitor binds to the active site of an enzyme, preventing the substrate from binding. This reduces the rate of reaction. Increasing the substrate concentration can overcome competitive inhibition.
How does a non-competitive inhibitor affect Vmax and Km?
Non-competitive inhibitors bind to an allosteric site on the enzyme, changing its shape and reducing its activity. Vmax is decreased because fewer functional enzyme molecules are available, and Km remains unchanged because the inhibitor does not affect substrate binding to the active sites that are still functional.
Outline two advantages of using immobilised enzymes.
Immobilised enzymes are more stable and can be reused, reducing costs. Also, the product is not contaminated with the enzyme, simplifying downstream processing.
Explain how increasing enzyme concentration affects the rate of reaction (assuming substrate is in excess).
When substrate is in excess, increasing the enzyme concentration increases the rate of reaction. This is because there are more active sites available to bind with substrate molecules, leading to more product formation per unit time.
Describe the effect of increasing substrate concentration on enzyme activity, assuming the enzyme concentration is constant.
Initially, increasing substrate concentration increases the rate of reaction as more active sites are occupied. However, as substrate concentration continues to increase, the rate plateaus, eventually reaching Vmax, because all active sites are saturated.
Review the material
Read full revision notes on Factors that affect enzyme activity — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 3 — Enzymes
Factors that affect enzyme activity sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Factors that affect enzyme activity deck
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