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Questions and Answers
What is the primary function of chymotrypsin in peptide bond cleavage?
What is the primary function of chymotrypsin in peptide bond cleavage?
Which step in the chymotrypsin mechanism involves a nucleophilic attack on the substrate?
Which step in the chymotrypsin mechanism involves a nucleophilic attack on the substrate?
What is a key aspect of acid-base catalysis in enzyme reactions?
What is a key aspect of acid-base catalysis in enzyme reactions?
What characteristic does metal ion catalysis provide to enzymatic reactions?
What characteristic does metal ion catalysis provide to enzymatic reactions?
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How are enzyme kinetics typically described?
How are enzyme kinetics typically described?
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Which of the following is NOT a reason for studying enzyme kinetics?
Which of the following is NOT a reason for studying enzyme kinetics?
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How do enzymes primarily increase the rate of reactions?
How do enzymes primarily increase the rate of reactions?
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In the context of chymotrypsin's mechanism, what occurs during the 'Water Attacks' step?
In the context of chymotrypsin's mechanism, what occurs during the 'Water Attacks' step?
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What factor is crucial in determining the overall rate of a reaction mediated by enzymes?
What factor is crucial in determining the overall rate of a reaction mediated by enzymes?
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In the context of enzyme catalysis, what does the transition state represent?
In the context of enzyme catalysis, what does the transition state represent?
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What is the significance of disulfide bonds in the structure of chymotrypsin?
What is the significance of disulfide bonds in the structure of chymotrypsin?
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What is meant by the term 'metastable intermediates' in enzyme reactions?
What is meant by the term 'metastable intermediates' in enzyme reactions?
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How do enzymes utilize binding energy during the catalysis process?
How do enzymes utilize binding energy during the catalysis process?
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Which enzyme is known for having a significant rate enhancement factor of 10^17?
Which enzyme is known for having a significant rate enhancement factor of 10^17?
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What characterizes uncatalyzed bimolecular reactions compared to catalyzed ones?
What characterizes uncatalyzed bimolecular reactions compared to catalyzed ones?
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In enzyme kinetics, what effect does the presence of a metal ion typically have on the reaction?
In enzyme kinetics, what effect does the presence of a metal ion typically have on the reaction?
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What is the effect of high substrate concentration ([S] >> Km) on the reaction order?
What is the effect of high substrate concentration ([S] >> Km) on the reaction order?
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Which parameter is considered the best measure of catalytic efficiency for enzymes?
Which parameter is considered the best measure of catalytic efficiency for enzymes?
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What is the significance of the Lineweaver-Burk plot in enzyme kinetics?
What is the significance of the Lineweaver-Burk plot in enzyme kinetics?
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In the context of enzyme kinetics, what does a higher value of kcat indicate?
In the context of enzyme kinetics, what does a higher value of kcat indicate?
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If an enzyme has a kcat/Km ratio close to 10^9 M^-1s^-1, what does this imply?
If an enzyme has a kcat/Km ratio close to 10^9 M^-1s^-1, what does this imply?
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What does the term Km represent in the Michaelis-Menten equation?
What does the term Km represent in the Michaelis-Menten equation?
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Which of the following enzymes does NOT achieve a kcat/Km near the diffusion-controlled limit?
Which of the following enzymes does NOT achieve a kcat/Km near the diffusion-controlled limit?
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In enzyme kinetics, the term 'Vmax' refers to which of the following?
In enzyme kinetics, the term 'Vmax' refers to which of the following?
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Why might the Km value be considered an important parameter in enzyme kinetics?
Why might the Km value be considered an important parameter in enzyme kinetics?
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Which type of catalysis involves the formation of a transient covalent bond between the enzyme and substrate?
Which type of catalysis involves the formation of a transient covalent bond between the enzyme and substrate?
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What is the primary function of metal ions in enzyme catalysis?
What is the primary function of metal ions in enzyme catalysis?
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Study Notes
Chymotrypsin
- Chymotrypsin is a protease that cleaves peptide bonds adjacent to aromatic amino acids.
- It has a ribbon structure with many β-sheets and some α-helices, stabilized by disulfide bonds.
Chymotrypsin Mechanism
- Step 1: Substrate Binding - The substrate binds to the active site of the enzyme.
- Step 2: Nucleophilic Attack - The enzyme's active site serine residue attacks the carbonyl carbon of the peptide bond.
- Step 3: Substrate Cleavage - The peptide bond is cleaved, forming a covalent intermediate between the enzyme and the substrate.
- Step 4: Water Comes In - A water molecule enters the active site.
- Step 5: Water Attacks - The water molecule attacks the carbonyl carbon of the intermediate.
- Step 6: Break-off from the Enzyme - The enzyme releases the cleaved product.
- Step 7: Product Dissociates - The product dissociates from the enzyme, leaving the enzyme free to bind another substrate.
Enzyme Kinetics
- Kinetics is the study of the rate of reactions.
- The rate of an enzymatic reaction is influenced by the enzyme, substrate, effectors, and temperature.
- Studying enzyme kinetics can help us understand the order of substrate binding, acid-base catalysis, catalytic mechanisms, find inhibitors, and understand the regulation of enzyme activity.
Derivation of Enzyme Kinetics Equations
- The simplest model mechanism is E + S ES E + P, with one reactant, one product, and no inhibitor.
- The total enzyme concentration is assumed to be constant.
- The total substrate concentration is usually much greater than the enzyme concentration.
- Enzymes increase reaction rates by decreasing activation energy.
Examples of Rate Enhancement by Enzymes
- Enzymes can increase reaction rates by several orders of magnitude.
- For example, carbonic anhydrase can increase the rate of CO2 hydration by 10^7 times.
- Orotidine monophosphate decarboxylase can increase the rate of its reaction by 10^17 times.
Reaction Coordinate Diagram
- The rate of a reaction is determined by the activation energy, or ΔG≠.
- The transition state is the configuration with the highest potential energy during the reaction.
- It is not to be confused with ES or EP complexes, which are reactive intermediates.
Enzymes Decrease ΔG≠
- Enzymes form metastable intermediates (ES and EP) with their substrates, lowering the activation energy.
- The rate-limiting step is the step with the highest activation energy, determining the overall rate of the reaction.
How Enzymes Lower ΔG≠
- Enzymes organize reactive groups into close proximity and orient them properly for optimal reaction.
- This organization makes the reaction entropically favorable, as the rigid ES complex lowers the entropy cost.
Michaelis-Menten Equation
- The Michaelis-Menten equation describes the relationship between the initial reaction velocity (V0), the substrate concentration ([S]), and the kinetic parameters Km and Vmax.
- At low [S], the reaction rate is linear and first order with respect to [S].
- At high [S], the reaction rate plateaus and becomes zero order with respect to [S].
Lineweaver-Burk Plot
- The Lineweaver-Burk plot is a linearized double-reciprocal plot of the Michaelis-Menten equation used for analyzing two-substrate data and enzyme inhibition.
Catalytic Efficiency (kcat/KM)
- kcat is the turnover number, the number of substrate molecules converted to product per enzyme molecule per second.
- Km is the Michaelis constant, the substrate concentration at which the reaction rate is half of Vmax.
- kcat/KM is a measure of the enzyme's efficiency in transforming substrate into product.
- Enzymes with high kcat/KM values are very efficient and can approach the diffusion-controlled limit, where the rate of reaction is limited by the diffusion of substrates and products.
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Description
This quiz explores the structure and function of chymotrypsin, a key protease enzyme. It covers the detailed mechanism of chymotrypsin from substrate binding to product dissociation, as well as its kinetic properties. Test your knowledge on enzymatic processes and chymotrypsin's role in proteolysis.
