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Questions and Answers
What is the role of the active site in an enzyme?
What distinguishes ribozymes from other enzymes?
In the standard chemical reaction at equilibrium, what does the ratio $k_1/k_{-1}$ represent?
Which equation represents the rate law for a reaction between two substrates A and B?
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What factor is represented by the constant k in the rate equations?
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What do enzymes primarily do in biochemical reactions?
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Which of the following describes the relationship between an enzyme and its substrate?
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What is a characteristic of the catalytic power of enzymes?
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Which term refers to the complete enzyme including its cofactor?
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How is the classification of enzymes primarily denoted?
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What does the term 'apoenzyme' refer to in enzyme terminology?
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Which factor does NOT influence enzyme activity?
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What role do cofactors play in enzyme functionality?
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What does a second-order reaction in rate law indicate?
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In the Michaelis-Menten model, what does the term Vmax represent?
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What is the rate-limiting step in the Michaelis-Menten equation?
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What assumption is made regarding k1 and k-1 in the Michaelis-Menten model?
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How is the equilibrium constant, Ks, defined in the context of the Michaelis-Menten equation?
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Which enzymes do not follow the Michaelis-Menten kinetics?
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What occurs at low substrate concentrations ([S]) in the context of the Michaelis-Menten model?
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If the substrate concentration is much greater than Ks, what does the rate v approach?
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What does the steady-state assumption imply in an enzyme-catalyzed reaction?
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What does the Michaelis constant (Km) represent in enzyme kinetics?
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Which of the following equations relates the concentration of enzyme-substrate complex (ES) to the total enzyme concentration ([E]total) and substrate concentration ([S])?
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Under what condition does the reaction velocity (v) reach its maximum (Vmax)?
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What effect does a high value of k-1 compared to k2 have on the Michaelis constant (Km)?
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Study Notes
Enzyme Kinetics Overview
- ΔG indicates the favorability of a reaction, while kinetics measures the rate of the reaction.
- Enzymes are crucial for kinetics, accelerating reaction rates significantly.
- Most enzymes are proteins that bind substrates at their active sites through weak interactions.
- The protonation of specific amino acids at the active site affects enzyme function.
Characteristics of Enzymes
- Enzymes catalyze favorable reactions, increasing rates by up to 10^21 times compared to uncatalyzed reactions.
- Typical reaction rates can range from 10^9 to 10^20 per second.
- High specificity (>95%) for substrates results from structural features at the active site.
Example of Enzyme Action: Urease
- Urease catalyzes the conversion of urea to ammonia.
- Uncatalyzed reaction rate: 3 x 10^-10/sec; catalyzed rate with urease: 3 x 10^4/sec.
- Catalytic power shows a ratio of 10^14 between catalyzed and uncatalyzed rates.
Enzyme Classification
- Enzymes often have a name based on their substrate with the suffix ‘ase’ (e.g., urease, protease).
- Official classification includes an E.C. number identifying class, subclass, and sub-subclass.
Key Terminology
- Apoenzyme: protein component of an enzyme.
- Holoenzyme: includes both the protein and cofactors.
- Cofactor: essential non-protein component for catalysis (e.g., metal ions).
- Coenzyme: non-protein organic molecule (e.g., B vitamins).
- Substrate: compound(s) that enzymes act upon.
- Active site: region where substrate binds for the reaction.
Unique Enzymes
- Ribozymes: RNA molecules with enzymatic activity, functioning without proteins (e.g., peptidyl transferase).
Kinetics Without Enzymes
- Initial rate of reaction represented as ( v = k[A] ), where ( k ) is the rate constant.
- At equilibrium, the ratio of products to reactants reaches a steady state.
Enzyme Kinetics
- For the reaction ( A + B \rightarrow P ):
- Rate law: ( v = k[A][B] ) indicating second-order kinetics.
- At low substrate concentrations, the rate is first-order; at high concentrations, it approaches Vmax (zero-order kinetics).
Michaelis-Menten Equation
- Describes enzyme-catalyzed reactions:
- ( S + E \rightleftharpoons ES \rightarrow E + P )
- Assumes rapid formation of the enzyme-substrate complex (ES) compared to product formation.
- Key assumptions include the breakdown of ES into products being slower than the formation of ES.
Steady State Condition
- In steady state, the formation and breakdown of ES are balanced; rate constants help define the Michaelis constant (Km).
- Equation for rate at steady state:
[ v = \frac{k_2[E]_{total}[S]}{K_m + [S]} ]
Vmax
- When substrate concentration is high (saturation), the reaction reaches its maximum rate ( Vmax ), where ( ES = [E]_{total} ).
- ( Vmax ) occurs when all enzyme active sites are occupied by substrate.
Allosteric Enzymes
- Allosteric enzymes differ from Michaelis-Menten kinetics; they exhibit sigmoidal kinetics due to multiple subunits and active sites.
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Description
Explore the fundamentals of enzyme kinetics, including the distinction between free energy and reaction rates. Discover how enzymes accelerate reactions, their specificity, and the significance of active site characteristics. This quiz provides insights into enzyme classification and their catalytic powers.
