Enzyme inhibition
Competitive inhibitors bind the active site and block the substrate. Non-competitive inhibitors bind elsewhere and change the enzyme's shape. Extra substrate can overcome competitive inhibition only.
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Analogy
A wrong key stuck in a lock versus a jammed door hinge.
In practice
Penicillin blocks a bacterial enzyme that builds cell walls. Ibuprofen blocks an enzyme that makes pain signals.
Practice
Flashcards
- How can you overcome competitive inhibition?Add more substrate so it outcompetes the inhibitor for the active site.
Interview questions
- Compare competitive and non-competitive inhibition, saying how each shows up on a rate-versus-substrate curve.
- Competitive binds the active site
- Non-competitive binds elsewhere
- Competitive: Vmax same, apparent Km rises
- Non-competitive: Vmax falls
Questions people ask
Are inhibitors always harmful?
No. Many medicines are enzyme inhibitors. Statins block an enzyme in cholesterol production, and ACE inhibitors lower blood pressure. The cell itself also uses inhibitors on purpose to control pathways. Harm comes when an inhibitor blocks an essential enzyme, as cyanide does with a respiration enzyme.
How is irreversible inhibition different?
A reversible inhibitor binds weakly and can come off again. An irreversible inhibitor forms a strong, usually covalent bond with the enzyme, permanently disabling it. Aspirin works this way on its target enzyme. The cell must make new enzyme molecules to recover its activity.