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Questions and Answers
What weak interactions primarily facilitate the formation of the enzyme-substrate complex?
What weak interactions primarily facilitate the formation of the enzyme-substrate complex?
What happens to the activation energy (DG‡) when an enzyme is present in a reaction?
What happens to the activation energy (DG‡) when an enzyme is present in a reaction?
In Michaelis-Menten kinetics, what happens to the initial reaction velocity (v0) at high substrate concentrations ([S])?
In Michaelis-Menten kinetics, what happens to the initial reaction velocity (v0) at high substrate concentrations ([S])?
What is the role of the active site in enzyme reactions?
What is the role of the active site in enzyme reactions?
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During the conversion of substrate A to product B, which state represents the molecule with the highest free energy?
During the conversion of substrate A to product B, which state represents the molecule with the highest free energy?
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What does the Michaelis constant, Km, indicate about the enzyme's activity?
What does the Michaelis constant, Km, indicate about the enzyme's activity?
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At what point does the enzyme reach maximum velocity (Vmax)?
At what point does the enzyme reach maximum velocity (Vmax)?
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Which of the following correctly describes the relationship between initial velocity (V0) and substrate concentration ([S])?
Which of the following correctly describes the relationship between initial velocity (V0) and substrate concentration ([S])?
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What does a higher Km value imply about an enzyme's affinity for its substrate?
What does a higher Km value imply about an enzyme's affinity for its substrate?
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In the context of the Michaelis-Menten equation, what is Vmax measured in?
In the context of the Michaelis-Menten equation, what is Vmax measured in?
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Study Notes
Enzyme Kinetics and Calculations
- Biochemistry studies the chemical processes within and relating to living organisms. Enzyme kinetics explores how enzymes catalyze biochemical reactions.
Chemical Kinetics: The Law of Mass Action
- Reaction rate is often directly proportional to reactant concentrations.
- For the reaction A → B, the reaction rate (v₀) is proportional to [A].
Effect of [A] on Initial Rate
- A linear relationship often exists between initial reaction rate (v₀) and reactant concentration ([A]).
- This implies a first-order reaction.
Enzyme Kinetics: Importance of Enzymes
- Life processes rely on proteins, with cells containing thousands of diverse enzymes for myriad reactions.
- Approximately 20,000 protein genes in the human genome are related to enzymes.
Enzymes as Biological Catalysts
- Enzymes significantly accelerate chemical reactions compared to uncatalyzed reactions.
- Enzyme speed enhancements range from 103 to 106 times faster.
Rate Enhancement by Some Enzymes
- Different enzymes vary greatly in their rate enhancements.
- Table provided shows examples like OMP Decarboxylase (1.4 x 1017), AMP nucleosidase (6.0 x 1012), and others.
Enzyme Mechanism
- Induced Fit: Substrates bind to the active site, inducing the enzyme to change shape, enfolding the substrate.
- Substrates are held in the active site via weak interactions (hydrogen bonds, ionic bonds)
- Active sites can lower the activation energy, speeding up the reaction.
- Products are subsequently released.
Michaelis-Menten Kinetics
- Michaelis and Menten proposed a model to describe substrate saturation in enzyme-catalyzed reactions.
- The model involves substrate (S) binding to enzyme (E) to form an enzyme-substrate complex (ES) which then breaks down into enzyme (E) and product (P).
Effect of Substrate Concentration on Rate
- At low substrate concentrations ([S]), the initial reaction velocity (v₀) is approximately proportional to [S].
- At high substrate concentrations ([S]), v₀ becomes independent of [S] due to enzyme saturation.
Michaelis-Menten Equation
- V₀ = (Vmax*[S]) / (Km + [S])
- V₀ : Initial velocity of a reaction
- Vmax : Maximum velocity of the reaction
- Km : Michaelis constant, [S] required for the reaction to proceed at Vmax/2.
- [S] : Substrate concentration
Meaning of Km and Vmax
- Km indicates the substrate dependency (typically 10-1 - 10-6M).
- Vmax represents the maximum rate of reaction. This is a measure of catalytic activity.
Units of Enzyme Activity
- Standard units: International Unit (IU, µmol/min)
- (SI unit): Katal (mol/sec) – a very large unit in practical terms.
Determining Km and Vmax
- Methods such as colorimetric assays are used for experimental determination of Km and Vmax.
Michaelis-Menten Plot & Problems
- Plots v₀ against [S] produce a hyperbolic curve approaching Vmax at high [S].
- Determining exact values for Vmax and Km is challenging from direct plots
Lineweaver-Burk Plot
- Transforming the Michaelis-Menten equation gives: 1/V₀ = (Km/Vmax) * (1/[S]) + 1/Vmax
- Plotting 1/V₀ against 1/[S] results in a straight line from which Km and Vmax can be determined.
Reaction Progress Curve
- Enzyme-catalyzed reactions show an initial phase of rapid increase in velocity that gradually plateaus.
Factors Affecting Reaction Rate
- Substrate availability decreases
- Product buildup: Reverse reaction becomes important.
- Enzyme degradation occurs.
Other Calculations for Kinetics
- Turnover Number (kcat): Represents the maximum catalytic activity of enzymes.
- The equation: Vmax/([Enzymetotal]).
Enzyme Characteristics: Summary
- Km and Vmax are key parameters defining an enzyme's behavior.
- Km reflects substrate affinity while Vmax represents overall efficiency.
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Description
This quiz delves into enzyme kinetics, focusing on how enzymes catalyze biochemical reactions and the relationship between reactant concentration and reaction rate. Understand the significance of enzymes as biological catalysts and their role in life processes. Test your knowledge on these essential concepts in biochemistry.
