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Questions and Answers
What is a characteristic feature of enzyme specificity?
What is a characteristic feature of enzyme specificity?
- Enzymes will catalyze multiple unrelated reactions.
- Enzymes are capable of acting on both stereoisomers of a compound.
- Enzymes typically possess a groove or cleft of defined shape. (correct)
- Enzymes generally have an active site for various types of substrates.
Which enzyme class includes enzymes that undergo oxidation-reduction reactions?
Which enzyme class includes enzymes that undergo oxidation-reduction reactions?
- Oxidoreductases (correct)
- Hydrolases
- Lyases
- Ligases
How are enzymes classified according to their functions?
How are enzymes classified according to their functions?
- Based on their reaction mechanisms alone.
- According to their molecular weight.
- According to the temperature at which they operate.
- By the type of reaction they catalyze. (correct)
Which of the following statements about enzyme-substrate interaction is true?
Which of the following statements about enzyme-substrate interaction is true?
What role does group specificity play in enzyme function?
What role does group specificity play in enzyme function?
What is true about enzymes that act on stereoisomers?
What is true about enzymes that act on stereoisomers?
What significant modification did Daniel Koshland propose to the lock and key theory?
What significant modification did Daniel Koshland propose to the lock and key theory?
Why is the lock and key model considered misleading?
Why is the lock and key model considered misleading?
What is the role of the transition state in enzymatic reactions?
What is the role of the transition state in enzymatic reactions?
How does the induced fit theory enhance enzyme activity?
How does the induced fit theory enhance enzyme activity?
What is a primary limitation of the lock and key model regarding enzyme function?
What is a primary limitation of the lock and key model regarding enzyme function?
What happens to an enzyme during substrate binding in the induced fit model?
What happens to an enzyme during substrate binding in the induced fit model?
In what way does an enzyme stabilize the transition state?
In what way does an enzyme stabilize the transition state?
Why is complementarity to the transition state critical for enzyme function?
Why is complementarity to the transition state critical for enzyme function?
What is the primary function of ligases in biochemical reactions?
What is the primary function of ligases in biochemical reactions?
Which enzyme is an example of an oxidoreductase?
Which enzyme is an example of an oxidoreductase?
What type of reaction do transferases catalyze?
What type of reaction do transferases catalyze?
Which of the following enzymes is a hydrolase?
Which of the following enzymes is a hydrolase?
What type of reaction do lyases catalyze?
What type of reaction do lyases catalyze?
Which product is formed from the action of lactate dehydrogenase?
Which product is formed from the action of lactate dehydrogenase?
What does alanine aminotransferase primarily do?
What does alanine aminotransferase primarily do?
Which molecule is a common substrate of trypsin?
Which molecule is a common substrate of trypsin?
Which of the following describes the action of DNA ligase?
Which of the following describes the action of DNA ligase?
Which statement accurately describes oxidoreductases?
Which statement accurately describes oxidoreductases?
What does the term Km represent in enzyme kinetics?
What does the term Km represent in enzyme kinetics?
How do competitive inhibitors affect the kinetic parameters of an enzyme?
How do competitive inhibitors affect the kinetic parameters of an enzyme?
Which of the following statements correctly defines irreversible inhibition?
Which of the following statements correctly defines irreversible inhibition?
What is the significance of the term Vmax in enzyme kinetics?
What is the significance of the term Vmax in enzyme kinetics?
What is the primary function of the active site of an enzyme?
What is the primary function of the active site of an enzyme?
Which model explains the specificity of enzyme-substrate interactions?
Which model explains the specificity of enzyme-substrate interactions?
What role do allosteric modulators play in enzyme function?
What role do allosteric modulators play in enzyme function?
Which of the following factors does not affect the rate of an enzyme-catalyzed reaction?
Which of the following factors does not affect the rate of an enzyme-catalyzed reaction?
Which factor is primarily responsible for the saturation of an enzyme reaction at high substrate concentrations?
Which factor is primarily responsible for the saturation of an enzyme reaction at high substrate concentrations?
In the Michaelis-Menten model, what does the 'ES' represent?
In the Michaelis-Menten model, what does the 'ES' represent?
What is the effect of enzyme inhibitors on reaction kinetics?
What is the effect of enzyme inhibitors on reaction kinetics?
What does the rate constant 'k2' represent in the Michaelis-Menten model?
What does the rate constant 'k2' represent in the Michaelis-Menten model?
At low substrate concentrations, the reaction rate is affected primarily by which of the following?
At low substrate concentrations, the reaction rate is affected primarily by which of the following?
Which assumption is NOT part of the Michaelis-Menten model?
Which assumption is NOT part of the Michaelis-Menten model?
What defines the hyperbolic kinetics observed in many enzyme reactions?
What defines the hyperbolic kinetics observed in many enzyme reactions?
Which statement best describes the term 'reaction rate' in the context of enzyme kinetics?
Which statement best describes the term 'reaction rate' in the context of enzyme kinetics?
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Study Notes
Properties of Enzymes and Enzyme Kinetics
- Enzymes are biological catalysts that accelerate reaction rates without changing the final equilibrium of the reactants and products.
- Catalase exemplifies enzyme efficiency, breaking down hydrogen peroxide (H2O2) to water at a rate 10^14 times faster than the uncatalyzed reaction at 30°C.
- Enzyme structure consists of one or more folded polypeptide chains stabilized by weak bonds such as hydrogen bonds, electrostatic interactions, Van der Waals forces, and hydrophobic interactions.
Enzyme Activity and Mechanisms
- Enzymes reduce activation energy barriers, facilitating reactions.
- Lock and key model: Proposed by Emil Fisher, where the enzyme is complementary to the substrate.
- Induced fit theory, introduced by Daniel Koshland, suggests that enzyme conformation changes upon substrate binding, optimizing the active site for catalysis.
Kinetics of Enzyme Reactions
- Initial velocity (v0), Km (Michaelis constant), and Vmax (maximum velocity) are crucial kinetic parameters.
- Michaelis-Menten equation describes the rate of enzyme-catalyzed reactions based on substrate concentration.
- Reaction rate is calculated by measuring the increase of product or decrease of substrate over time.
- Many enzymes exhibit hyperbolic kinetics: at low substrate concentrations, velocity is directly proportional to substrate concentration; at high concentrations, the rate approaches Vmax and becomes independent of substrate concentration.
Enzyme Inhibition
- Competitive inhibitors bind to the active site, increasing Km (the concentration of substrate needed to reach half of Vmax) without changing Vmax.
- Non-competitive inhibitors bind elsewhere on the enzyme, reducing Vmax while leaving Km unchanged.
- Reversible inhibition can be reversed by removing the inhibitor, whereas irreversible inhibition permanently inactivates the enzyme.
Enzyme Regulation
- Allosteric modulation involves changes in enzyme activity due to binding at sites other than the active site. Allosteric activators enhance activity while inhibitors decrease it.
- Cooperativity refers to the phenomenon where the binding of a substrate to one active site influences the binding properties of other active sites on the enzyme.
Substrate Specificity and Classification
- Enzymes demonstrate specificity, often catalyzing one type of reaction and acting on related molecules (group specificity).
- Classification by the International Union of Biochemistry (I.U.B.) categorizes enzymes into six main classes based on their catalytic activities:
- Oxidoreductases: Catalyze oxidation/reduction reactions (e.g., lactate dehydrogenase).
- Transferases: Transfer functional groups between substrates (e.g., alanine aminotransferase).
- Hydrolases: Catalyze hydrolytic reactions (e.g., trypsin).
- Lyases: Catalyze non-hydrolytic additions or removals of groups.
- Ligases: Join molecules through the synthesis of new bonds, coupled with ATP hydrolysis.
Key Terms
- Enzyme-substrate complex (ES): The intermediate formed when a substrate binds to the enzyme.
- Transition state: A high-energy state during a reaction that enzymes help stabilize, lowering activation energy.
- Km: Reflects the substrate concentration at which the reaction rate is half of Vmax; important for assessing enzyme efficiency.
- Vmax: Maximum reaction rate achieved by an enzyme at saturation with substrate.
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