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Questions and Answers
What is formed when the substrate binds to the enzyme?
What is formed when the substrate binds to the enzyme?
How do catalysts affect the rate of a reaction?
How do catalysts affect the rate of a reaction?
Which statement is true regarding the transition state of a reaction?
Which statement is true regarding the transition state of a reaction?
What does ΔG‡ represent in a chemical reaction?
What does ΔG‡ represent in a chemical reaction?
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Which factor can increase reaction rates apart from adding a catalyst?
Which factor can increase reaction rates apart from adding a catalyst?
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What effect do enzymes have on the standard free-energy change (ΔG’) of a reaction?
What effect do enzymes have on the standard free-energy change (ΔG’) of a reaction?
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How does the presence of an appropriate enzyme influence the reaction equilibrium?
How does the presence of an appropriate enzyme influence the reaction equilibrium?
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In enzyme-catalyzed reactions, what is the primary role of the enzyme?
In enzyme-catalyzed reactions, what is the primary role of the enzyme?
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What is indicated by the first digit of an enzyme's EC number?
What is indicated by the first digit of an enzyme's EC number?
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Which of the following describes an apoenzyme?
Which of the following describes an apoenzyme?
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What role do coenzymes play in enzyme activity?
What role do coenzymes play in enzyme activity?
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What characterizes a holoenzyme?
What characterizes a holoenzyme?
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Which of the following metal ions is commonly considered as a cofactor for enzymes?
Which of the following metal ions is commonly considered as a cofactor for enzymes?
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What describes the active site of an enzyme?
What describes the active site of an enzyme?
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How does an enzyme-catalyzed reaction differ from an uncatalyzed reaction under physiological conditions?
How does an enzyme-catalyzed reaction differ from an uncatalyzed reaction under physiological conditions?
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Which of the following processes occurs during enzyme catalysis?
Which of the following processes occurs during enzyme catalysis?
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What primarily contributes to the specificity of enzymes towards their substrates?
What primarily contributes to the specificity of enzymes towards their substrates?
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What phenomenon describes the conformational change of an enzyme upon substrate binding?
What phenomenon describes the conformational change of an enzyme upon substrate binding?
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How does binding energy assist in enzymatic reactions?
How does binding energy assist in enzymatic reactions?
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What is the result of desolvation of the substrate when it binds to an enzyme?
What is the result of desolvation of the substrate when it binds to an enzyme?
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Which of the following factors aids in increasing the number of productive collisions in enzymatic reactions?
Which of the following factors aids in increasing the number of productive collisions in enzymatic reactions?
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What defines a reaction intermediate?
What defines a reaction intermediate?
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What is the significance of the rate-limiting step in a reaction?
What is the significance of the rate-limiting step in a reaction?
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Which statement correctly describes the relationship between activation energy and reaction rate?
Which statement correctly describes the relationship between activation energy and reaction rate?
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In enzyme-catalyzed reactions, what does the enzyme complementarity to the substrate imply?
In enzyme-catalyzed reactions, what does the enzyme complementarity to the substrate imply?
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How is the equilibrium constant denoted in biochemical processes?
How is the equilibrium constant denoted in biochemical processes?
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Which equation relates the rate constant and activation energy in enzyme catalysis?
Which equation relates the rate constant and activation energy in enzyme catalysis?
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What occurs if there is no energy barrier in a reaction?
What occurs if there is no energy barrier in a reaction?
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What is the function of the ES complex in the reaction pathway?
What is the function of the ES complex in the reaction pathway?
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What is the role of binding energy in the transition state during an enzyme-catalyzed reaction?
What is the role of binding energy in the transition state during an enzyme-catalyzed reaction?
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How does the formation of covalent bonds during an enzyme-catalyzed reaction affect activation energy?
How does the formation of covalent bonds during an enzyme-catalyzed reaction affect activation energy?
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What types of weak interactions are important in the formation of the ES complex?
What types of weak interactions are important in the formation of the ES complex?
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What is the significance of the net activation energy in enzyme-catalyzed reactions?
What is the significance of the net activation energy in enzyme-catalyzed reactions?
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In what way do non-covalent interactions contribute to catalysis?
In what way do non-covalent interactions contribute to catalysis?
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Why must an enzyme precisely position functional groups within the active site?
Why must an enzyme precisely position functional groups within the active site?
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What range of rate enhancements can enzymes typically achieve?
What range of rate enhancements can enzymes typically achieve?
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How does the active site of an enzyme contribute to the catalysis process?
How does the active site of an enzyme contribute to the catalysis process?
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Study Notes
Enzyme Classification
- Each enzyme is assigned a unique EC number based on its reaction type.
- First digit indicates the main class: oxidoreductase (1), transferase (2), etc.
- Second digit specifies the subclass of reaction.
- Third digit details the specific group transferred or bond cleaved.
- Fourth digit is the unique identifier within the sub-subclass.
- Example: ATP glucose phosphotransferase/hexokinase is EC 2.7.1.1 (transferase, phosphotransferase).
Enzyme Cofactors
- Cofactor: non-protein chemical component essential for enzyme activity.
- Metal ions (e.g., Fe²⁺, Mg²⁺, Mn²⁺, Zn²⁺) are important inorganic cofactors.
- Coenzymes: complex organic or metalloorganic compounds that assist enzymes.
- Prosthetic groups are tightly bound coenzymes or metal ions to enzymes.
- Holoenzyme: active enzyme with its cofactor; apoenzyme refers to the protein part minus its cofactor.
Enzymatic Activity
- Uncatalyzed reactions are typically slow under physiological conditions (neutral pH, mild temperature).
- Enzymes create a specific environment for reactions within the active site, a pocket in the enzyme.
- Active site's amino acid residues interact with substrates, forming an enzyme-substrate complex.
Enzyme-Catalyzed Reactions
- Catalysts increase reaction rates without altering equilibria.
- Ground state refers to the starting point of a reaction; ΔG° indicates standard free-energy change under specific conditions.
- Transition state represents the highest energy state along the reaction pathway, with ΔG‡ as the activation energy.
- Energy barriers need to be overcome for the conversion of substrate (S) to product (P).
Reaction Intermediates
- Reaction intermediates are species with finite lifetimes beyond molecular vibrations.
- ES (enzyme-substrate) and EP (enzyme-product) complexes are considered intermediates.
- The rate-limiting step in a reaction is often the highest energy point in the pathway.
Rate of Reaction
- Reaction rate is influenced by reactant concentrations and rate constants (k).
- For unimolecular reactions, V = k[S]; for bimolecular reactions, V = k[S1][S2].
- The Eyring-Polanyi equation relates rate constant k with activation energy ΔG‡, incorporating temperature and constants for Boltzmann (kB) and Planck (h).
Mechanism of Enzyme-Catalyzed Reactions
- Enzymes fit their substrates like a lock and key, being structurally complementary.
- These interactions may not allow substrates to reach the transition state effectively without aid from enzyme interactions.
- Enzyme must be complementary to the transition state to facilitate the reaction.
Rate Enhancements by Enzymes
- Enzymes enhance reaction rates by 5 to 17 orders of magnitude.
- Rearrangements of covalent bonds during reactions lower activation energy by creating alternative pathways.
- Non-covalent interactions stabilize the ES complex and contribute to catalytic efficiency.
Binding Energy and Reaction Specificity
- Enzymatic specificity arises from numerous weak interactions between enzyme and substrate.
- Enzymes can discriminate between substrates based on the strength and type of binding.
- Binding energy, released during substrate-enzyme interactions, is crucial in stabilizing the transition state.
Physical and Thermodynamic Factors
- Enzymes reduce the entropy of substrates, enhancing the likelihood of productive collisions.
- Proper alignment of enzyme functional groups is critical for catalytic activity.
- Induced fit: enzyme conforms to the substrate upon binding, facilitating reaction.
- Enzyme-substrate interactions often replace solvation shells formed by water, promoting effective catalysis.
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Description
This quiz covers the basics of enzyme classification, including the EC number system which categorizes enzymes based on the reactions they catalyze. It also explores the example of a biochemical reaction involving ATP. Test your understanding of these fundamental concepts!
