Enzymes and Metabolic Reactions
Explaining enzyme specificity, induced fit, activation energy, rate effects, inhibition and the design and interpretation of enzyme investigations.
How to study A-level Biology
Move between scales deliberately: identify the biological process, trace matter or information, use quantitative evidence, then evaluate the method and conclusion.
Core concepts
Concept 1
An enzyme's tertiary structure forms an active site whose chemistry and shape enable specific substrate binding and catalysis.
Exam cue: Explain a rate change using collisions, enzyme-substrate complexes and limiting factors.
Concept 2
Temperature, pH, enzyme concentration and substrate concentration affect rate through collision frequency or protein structure.
Exam cue: Distinguish reversible changes in rate from denaturation caused by altered tertiary structure.
Concept 3
Competitive and non-competitive inhibitors change enzyme activity through different binding interactions and concentration effects.
Exam cue: Use an initial rate or a defined endpoint and keep all relevant conditions constant.
Risk pitfalls and guardrails
Saying high temperature kills an enzyme rather than altering its structure.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Assuming all inhibition can be overcome by more substrate.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Equating a plateau with the enzyme having stopped working without identifying the limiting factor.
Guardrail: Do not replace a mechanism with a vague purpose statement, or infer causation from an association without experimental support.
Memory anchors
Activation Energy
Enzymes increase reaction rate by lowering activation energy.
Induced Fit
Substrate binding changes the active site into a catalytically effective fit.
Denaturation
Denaturation changes protein tertiary structure and therefore active-site function.
Competitive Inhibitor
A competitive inhibitor binds at the active site and competes with substrate.
Initial Rate
Initial rate is measured before substantial substrate depletion or product accumulation.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
How does an enzyme increase reaction rate?
Which statement best describes induced fit?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”