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Questions and Answers
What does the term Km represent in Michaelis-Menten kinetics?
Which plot is used to visualize the relationship between the substrate concentration and the reaction rate in Michaelis-Menten kinetics?
What effect do enzyme inhibitors have on enzymatic reactions?
In the context of enzyme kinetics, what does the term Vmax refer to?
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Which of the following describes a characteristic of reversible enzyme inhibition?
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What happens to Km in competitive inhibition?
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Which type of inhibition results in both decreased Km and Vmax?
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In mixed inhibition, when KI < K'I, what is the effect on Km?
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Which type of inhibition allows the Vmax to remain unaffected?
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What characterizes noncompetitive inhibition?
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What is a characteristic feature of uncompetitive inhibitors?
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When comparing mixed inhibition and noncompetitive inhibition, what is a key difference?
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How is the equilibrium constant KI defined in the context of inhibition?
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Study Notes
Enzyme Kinetics
- Enzyme kinetics is the study of the rates of enzymatic reactions.
- Michaelis-Menten (MM) kinetics is a model that describes the behavior of enzymes based on substrate concentration.
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MM equation: v = (Vmax * [S]) / (Km + [S]) where:
- v is the reaction rate
- Vmax is the maximum possible reaction rate
- [S] is the substrate concentration
- Km is the Michaelis constant, which is the substrate concentration at which the reaction rate is half of Vmax.
- The Michaelis-Menten plot shows the relationship between reaction rate and substrate concentration.
- The Lineweaver-Burk plot is the double reciprocal plot of the Michaelis-Menten equation, which allows for easier determination of Km and Vmax.
Enzyme Inhibition
- Enzyme inhibitors are compounds that reduce the rate of an enzymatic reaction.
- Reversible inhibition: binds to the enzyme through non-covalent interactions (can be reversed).
- Irreversible inhibition: binds to the enzyme through covalent interactions (can't be reversed)
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Types of reversible inhibition:
- Competitive inhibition: Inhibitor competes with substrate for the active site of the enzyme.
- Uncompetitive inhibition: Inhibitor binds to the enzyme-substrate complex (ES), not the free enzyme (E).
- Mixed inhibition: Inhibitor binds to both the free enzyme (E) and the enzyme-substrate complex (ES).
- Noncompetitive inhibition: Inhibitor binds with the same affinity to both the free enzyme (E) and the enzyme-substrate complex (ES).
Competitive Inhibition
- Mechanism: The inhibitor resembles the substrate and binds to the active site, preventing substrate binding.
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Lineweaver-Burk plot impact:
- Km increases (because more substrate is needed to reach half Vmax)
- Vmax remains unchanged (because the inhibitor doesn't affect the maximum reaction rate).
Uncompetitive Inhibition
- Mechanism: The inhibitor binds to a site distinct from the active site, only when the substrate is already bound to the enzyme.
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Lineweaver-Burk plot impact:
- Km decreases (because the inhibitor stabilizes the ES complex)
- Vmax decreases (because the inhibitor decreases the number of active enzyme-substrate complexes).
Mixed Inhibition
- Mechanism: The inhibitor binds to a site distinct from the active site, and can bind to both free enzyme (E) and the enzyme-substrate complex (ES).
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Lineweaver-Burk plot impact:
- If KI < K’I (inhibitor binds more strongly to free enzyme E), Km increases.
- If KI > K’I (inhibitor binds more strongly to the ES complex), Km decreases.
- Vmax decreases (because the inhibitor reduces the number of functional enzyme molecules).
Noncompetitive Inhibition
- Mechanism: The inhibitor binds to a site distinct from the active site, and binds equally well to both the free enzyme (E) and enzyme-substrate complex (ES).
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Lineweaver-Burk plot impact:
- Km remains unchanged (because the inhibitor doesn't affect the substrate binding).
- Vmax decreases (because the inhibitor reduces the number of active enzyme molecules).
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Description
This quiz covers the fundamentals of enzyme kinetics, including Michaelis-Menten kinetics and its equations. Explore the concepts of Vmax, Km, and the graphical representations such as the Michaelis-Menten and Lineweaver-Burk plots. Additionally, review the types of enzyme inhibition, distinguishing between reversible and irreversible inhibition.
