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3.2.73 · Enzymes

Enzyme Inhibitors — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions

5 min read 8 parts Lesson 15 of 17 1 quiz

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

3.2.7 Enzyme Inhibitors — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Describe reversible inhibitors and end-product inhibition.Effect — they reduce or stop enzyme activity temporarily.Binding — they bind with weak non-covalent bonds and can leave the enzyme.Shape…

  • Effect on kinetics
  • Binding site
  • Competitive inhibitor
  • Feedback loop
  • Metabolic pathway
  • Shape — the inhibitor has a shape similar to the substrate

Part 1 of 6Reversible inhibitors

Effect
  • Effect they reduce or stop enzyme activity temporarily.
Binding
  • Binding they bind with weak non-covalent bonds and can leave the enzyme.

Part 2 of 6Competitive inhibition

Shape
  • Shape the inhibitor has a shape similar to the substrate.
Mechanism
  • Mechanism it competes with the substrate for the active site.
Effect on kinetics
  • Vmax can still be reached with enough substrate, but Km increases.

Part 3 of 6Non-competitive inhibition

Binding site
  • Binding site the inhibitor binds to an alternative site on the enzyme.
Mechanism
  • Mechanism it changes the shape of the active site so the substrate cannot bind.
Effect on kinetics
  • Vmax falls and Km is unchanged.

Part 4 of 6End-product inhibition

Principle
  • Principle the end-product of a metabolic sequence acts as a reversible non-competitive inhibitor of an earlier enzyme.
Purpose
  • Purpose metabolic reactions must be tightly controlled, so no enzyme runs out of control.

Part 5 of 6Steps in end-product inhibition

1
The enzyme converts substrate to product.
2
As product builds up, it binds to an alternative site on the original enzyme.
3
The active site changes shape and no more enzyme–substrate complexes form.
4
The end-product detaches and is used elsewhere.
5
The active site reforms, so the enzyme becomes active again when product levels fall.
  • Result
    • a continuous feedback loop.

Part 6 of 6More from the specification

1Enzyme inhibition kinetics
  • Enzyme inhibition kinetics plotting Lineweaver-Burk double reciprocal plots provides a clear diagnostic means to distinguish competitive from non-competitive inhibitors.
2Competitive enzyme inhibition
  • Competitive inhibitors resemble the substrate and compete for active site binding, raising Km without altering maximum velocity (Vmax).
3Non-competitive allosteric inhibition
  • Non-competitive inhibitors bind to allosteric sites, altering active site conformation and lowering Vmax regardless of substrate concentration.
4Substrate concentration effects on inhibition
  • Increasing substrate concentration overcomes competitive inhibition, but cannot reverse non-competitive catalytic reduction.
5Non-competitive allosteric binding
  • Non-competitive allosteric binding non-competitive inhibitors bind to allosteric sites, altering active site geometry and decreasing Vmax.
6End-product inhibition control
  • End-product inhibition control accumulation of reaction product molecules reversibly inhibits initial pathway enzymes to regulate metabolic flux.
7Immobilised enzymes in industry
  • Immobilised enzymes in industry immobilised enzymes resist denaturation at elevated temperatures and enable continuous commercial production.
8Affinity
  • How readily haemoglobin binds oxygen.
9Buffer
  • A substance that resists pH change by absorbing or releasing H+.
10Substrate concentration
  • The amount of substrate per unit volume.
11Enzyme concentration
  • The amount of enzyme per unit volume.
12Successful collision
  • A collision with enough energy and correct orientation.
13Immobilised enzyme
  • An enzyme fixed to a surface or trapped in a matrix so it can be reused.
14Buffer solution
  • A solution that holds the pH at a fixed value.
15Enzyme-substrate complex
  • The temporary structure formed when a substrate binds to an enzyme's active site.
16Constants
  • Factors deliberately kept the same so the result has one cause.
17Lactose
  • A disaccharide of glucose and galactose.
18Optimum
  • The temperature or pH at which activity is highest.

Key terms

TermMeaning
Reversible inhibitorAn inhibitor that binds temporarily to an enzyme.
Competitive inhibitorAn inhibitor that competes for the active site.
Non-competitive inhibitorAn inhibitor that binds at another site and alters the active site.
End-product inhibitionControl of a pathway by its end-product inhibiting an earlier enzyme.
Feedback loopA control system in which the output regulates the process.
Metabolic pathwayA sequence of enzyme-catalysed reactions.

Avoid these mistakes

1
Saying inhibitors permanently damage the enzyme — reversible inhibitors can detach.
2
Saying competitive inhibitors bind at another site — they bind at the active site.
3
Saying end-product inhibition is competitive — it is non-competitive.
4
Forgetting that Km changes only for competitive inhibition — non-competitive leaves Km unchanged.

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