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3.2.43 · Enzymes

Rate- Substrate Concentration — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 7 parts Lesson 12 of 17 1 quiz

📚 Cambridge AS & A Level Biology 9700 Hub / Topical Revision
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Lesson summary

3.2.4 Rate: Substrate Concentration — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Explain how substrate concentration affects the rate of reaction and what causes the plateau.Higher rate — more substrate molecules make enzyme–substrate complexes more likely.Fixed …

  • Fixed enzyme
  • Linear section
  • Saturation
  • No more binding
  • Limiting factor
  • Initial phase

Part 1 of 5Rising substrate concentration

Higher rate
  • Higher rate more substrate molecules make enzyme–substrate complexes more likely.
Fixed enzyme
  • Fixed enzyme this holds while the enzyme concentration is kept constant.
Linear section
  • Linear section rate increases in proportion to substrate concentration at low concentrations.

Part 2 of 5Saturation of active sites

Saturation
  • Saturation beyond a certain point all active sites are occupied.
No more binding
  • No more binding extra substrate molecules have nowhere to bind.
Plateau
  • Plateau the rate stops increasing until active sites become free again.

Part 3 of 5Maximum rate

Queuing
  • Queuing substrate molecules effectively wait for an active site to become free.
Vmax
  • Vmax the enzyme works at its maximum possible rate, the maximum velocity.
Limiting factor
  • Limiting factor at the plateau, enzyme concentration becomes limiting.

Part 4 of 5Reading the graph

1Initial phase
  • Initial phase a linear rise as substrate increases.
2Final phase
  • Final phase a plateau when all active sites are in use.

Part 5 of 5More from the specification

More from the specification
Enzymatic product formation rate
  • Enzymatic product formation rate increasing substrate concentration elevates initial reaction velocity until all active sites become saturated, providing a means of control.
Lactose
  • A disaccharide of glucose and galactose.
Optimum
  • The temperature or pH at which activity is highest.
Affinity
  • How readily haemoglobin binds oxygen.
Buffer
  • A substance that resists pH change by absorbing or releasing H+.
Successful collision
  • A collision with enough energy and correct orientation.
Immobilised enzyme
  • An enzyme fixed to a surface or trapped in a matrix so it can be reused.
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.
Competitive inhibitor
  • Competitive inhibitor it fits the active site and blocks the substrate, so its effect lessens as substrate concentration rises.
Non-competitive inhibitor
  • Non-competitive inhibitor it binds elsewhere and changes the active site, lowering the maximum rate even when substrate is plentiful.

Key terms

TermMeaning
SaturationAll active sites occupied by substrate.
VmaxThe maximum rate of an enzyme-catalysed reaction.
Limiting factorThe factor restricting the rate.
Enzyme–substrate complexThe temporary complex formed at the active site.
Active siteThe region where the substrate binds.
VelocityThe speed of the reaction.

Avoid these mistakes

1
Saying the rate keeps rising with substrate — it plateaus at saturation.
2
Explaining the plateau by lack of substrate — it is because the active sites are all occupied.
3
Forgetting to name the limiting factor at the plateau — it is enzyme concentration.
4
Saying Vmax changes with substrate concentration — it is the maximum at saturation.

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