Questions and Answers
Increasing substrate concentration restores enzyme activity that has been blocked by which type of inhibitor?
What happens to the initial reaction velocity, V0, of penicillinase if the penicillin concentration is 10.4×10−6 M?
The initial reaction velocity would approach Vmax.
What effects are produced by an enzyme on a general reaction?
Enzymes increase reaction rates, lower activation energy, and promote the formation of transition states.
For a specific enzyme/substrate system, which condition will always result in an increase in V0 ?
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The rate-limiting step of an enzyme-catalyzed reaction has which characteristic?
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What is the effect of competitive inhibitors on an enzyme's Km and Vmax?
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What does the Michaelis-Menten equation model?
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Study Notes
Enzyme Activity and Inhibition
- Competitive inhibitors resemble the substrate and compete for the active site, allowing increased substrate concentration to reverse their effects.
- Noncompetitive inhibitors bond outside the active site, altering its shape, so increased substrate concentration does not restore enzyme activity.
Penicillinase Kinetics
- Penicillinase hydrolyzes penicillin and follows Michaelis-Menten kinetics.
- At a penicillin concentration of 5.2×10−6 M, the initial reaction velocity (V0) reaches half maximum (6.8×10−10 µmol⋅min−1).
- Doubling penicillin concentration to 10.4×10−6 M approaches Vmax, reflecting hyperbolic reaction velocity behavior characteristic of Michaelis-Menten kinetics.
Enzyme Function
- Enzymes are catalysts that enhance reaction rates without undergoing permanent change.
- They facilitate the formation of transition states and lower activation energy, thereby increasing reaction rates for both forward and reverse reactions.
- Enzymes do not alter the equilibrium position or change the free energy difference (ΔG) of reactants and products.
Factors Affecting Reaction Velocity
- An increase in substrate concentration ([S]) consistently increases V0 if other factors remain constant.
- A decrease in Km (Michaelis constant) and an increase in Vmax (maximal rate) lead to higher V0.
Rate-Limiting Step in Reactions
- The rate-limiting step of an enzyme reaction is defined by the rate constant kcat and is not necessarily the final or fastest step.
Types of Enzyme Inhibition
- Competitive inhibitors increase KM without changing Vmax, directly competing with the substrate for the active site.
- Uncompetitive inhibitors lower both KM and Vmax by binding to the enzyme-substrate complex.
- Noncompetitive inhibitors decrease Vmax with no impact on KM, binding to either the enzyme or the enzyme-substrate complex.
Michaelis-Menten Equation Insights
- The Michaelis-Menten equation describes the relationship between substrate concentration and reaction velocity under steady-state conditions.
- When [S] equals KM, V0 equals half of Vmax, indicating half of the enzyme's active sites are occupied.
- At high substrate concentrations ([S] >> KM), the enzyme is primarily in the enzyme-substrate complex (ES), resulting in a maximum rate (Vmax).
Conditions Based on Substrate Concentration
- For [S] = KM, half of the active sites are occupied, yielding V0 = Vmax/2.
- For [S] >> KM, the reaction reaches Vmax, becoming independent of substrate concentration as all active sites are occupied.
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Description
This quiz focuses on the concepts of enzyme inhibition, specifically competitive inhibitors and their relationship with substrate concentration. It aims to reinforce understanding through flashcard-format questions and definitions. Ideal for students reviewing lecture notes from Biochemistry Lectures 4 and 5.
