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RELEVANT LEARNING OUTCOME:
(c) Describe the structure of competitive and non-competitive inhibitors with reference to the binding sites of the inhibitor. [H2 only]
(d) Explain the effects of competitive and non-competitive inhibitors (including allosteric inhibitors) on the rate of enzyme activity. [H2 only]
Enzyme inhibitors acting as drugs
Enzyme inhibitors acting as drugs
A competitive inhibitor can be used as drugs to treat diseases. Some examples in the real-world context are Tamiflu (Oseltamivir) – Inhibits neuraminidase, blocking influenza virus replication. Ibuprofen & Aspirin – Competitively inhibit cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis for pain relief.
Similarly, non-competitive inhibitors like Monoamine Oxidase Inhibitors are antidepressants used to treat depression and Parkinson’s disease.
Effect of competitive inhibition on rate of reaction
Effect of competitive inhibition on rate of reaction
👁️🗨️ Watch the video from 0:00 to 2:22 for the effect of competitive inhibitor on the maximum rate of reaction. The terms Km and Vmax are explained using the graph.
🖊️Check Your Understanding: Lecture notes Checkpoint
🖊️Check Your Understanding: Lecture notes Checkpoint
Both competitive inhibitor and non-competitive inhibitor binds to enzyme to form ___________complex.
Both competitive inhibitor and non-competitive inhibitor binds to the enzyme to form enzyme-inhibitor complex.
2. Both competitive inhibitor and non-competitive inhibitor ___________ rate of enzyme catalysed reaction.
Both competitive inhibitor and non-competitive inhibitor reduces rate of enzyme catalysed reaction.
3. Structure of competitive inhibitor ____________ substrate whereas structure of non-competitive inhibitor ______________________________ substrate.
3. Structure of competitive inhibitor ____________ substrate whereas structure of non-competitive inhibitor ______________________________ substrate.
Structure of competitive inhibitor resembles substrate whereas structure of non-competitive inhibitor does not resemble substrate.
Structure of competitive inhibitor resembles substrate whereas structure of non-competitive inhibitor does not resemble substrate.
4. Competitive inhibitor binds to the _____________________ of the enzyme. The bonding is temporary whereas non-competitive inhibitor binds to enzyme at a ____________________________________________________. The binding is permanent.
Competitive inhibitor binds to the active site of the enzyme. The bonding is temporary whereas non-competitive inhibitor binds to enzyme at a region other than the active site. The binding is permanent.
5. Effect of increasing substrate concentration on inhibition of rate of reaction:
Competitive inhibition can be ______________ because substrate molecules can displace the inhibitor from the active site of enzyme.
No effect for non-competitive inhibition as the bonding between the enzyme and inhibitor can be ______________________.
Effect of increasing substrate concentration on inhibition of rate of reaction:
Competitive inhibition can be reversed because substrate molecules can displace the inhibitor from the active site of enzyme.
No effect for non-competitive inhibition as the bonding between the enzyme and inhibitor can be irreversible.
6. Reason for decreased rate of reaction:
Competitive inhibition: __________________ number of free active sites available for the genuine substrates to bind and form ES complexes.
Non-competitive inhibition: Change in the ______________________ of the enzyme (including active site) such that substrate can no longer bind to active site.
Reason for decreased rate of reaction:
Competitive inhibition: Decreased number of free active sites available for the genuine substrates to bind and form ES complexes.
Non-competitive inhibition: Change in the configuration of the enzyme (including active site) such that substrate can no longer bind to active site.
7. For competitive inhibition, at very high substrate concentration, the maximum rate of reaction in the presence of inhibitor can be _____________________ to that of reaction in the absence of inhibitor
For non-competitive inhibition, even at very high substrate concentration, the maximum rate of reaction in the presence of inhibitor is _____________________ that of reaction in the absence of inhibitor.
For competitive inhibition, at very high substrate concentration, the maximum rate of reaction in the presence of inhibitor can be very close to that of reaction in the absence of inhibitor
For non-competitive inhibition, even at very high substrate concentration, the maximum rate of reaction in the presence of inhibitor is less than that of reaction in the absence of inhibitor.
8. Graph showing effect of the inhibitor on relationship between rate of reaction and substrate concentration
* Graph for non-competitive inhibitor is for irreversible binding only
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