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Questions and Answers
What are the units of first-order rate constants and how do they differ from second-order constants?
The units of first-order rate constants are s⁻¹, whereas second-order constants have units of M⁻¹s⁻¹.
Explain the significance of the Michaelis constant (Km) in enzyme kinetics.
Km is the substrate concentration at which the reaction velocity (v) is half of the maximum velocity (vmax).
What is the turnover number (kcat) in enzyme kinetics and why is it important?
The turnover number (kcat) is the maximum number of substrate molecules converted to product per enzyme molecule per unit time, and it is crucial for understanding enzyme efficiency.
How does allosteric regulation differ from competitive inhibition in enzyme activity?
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Describe the relationship between Vmax and total enzyme concentration ([E]T) in Michaelis-Menten kinetics.
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What distinguishes allosteric enzymes from traditional enzymes in terms of their active sites?
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How is the value of $K_M$ determined using a Lineweaver-Burk plot?
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What effect does an allosteric inhibitor have on the active sites of an allosteric enzyme?
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In Eadie-Hofstee diagrams, how is $V_{max}$ represented?
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What is an example of a substrate that acts as an allosteric activator?
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Study Notes
Enzymes: Remarkable Catalysts
- Enzymes speed up biochemical reactions.
- Most enzymes are proteins, some are RNA.
- Enzymes stabilize transition states (highest-energy species in reaction pathways).
- Enzymes work in specific temperature and pH ranges.
Enzyme-Catalyzed Reactions
- Reactants are called substrates.
- Enzymes are highly specific; proteolytic enzymes hydrolyze peptide bonds.
Active Sites of Enzymes
- Enzymes have catalytic and binding sites.
- Catalytic site is where the chemical reaction occurs (converts substrates to products).
- Binding site (active site) is where the substrate binds to the enzyme, creating an enzyme-substrate complex. This binding is highly specific.
- The induced-fit model of enzyme-substrate binding suggests the active site changes shape to complement the substrate upon binding. (Lock-and-key model suggests the active site is complementary in shape to the substrate)
Cofactors for Enzyme Activity
- Cofactors are non-protein molecules or ions (coenzymes or metals) that assist in catalysis.
- Enzymes and their cofactors lower activation energy.
- Cofactors are essential for enzyme function; their absence can lead to decreased activity or malfunction.
- Holoenzyme is an enzyme with its cofactor; apoenzyme is an enzyme without its cofactor.
Thermodynamics and Enzymes
- Change in Gibbs free energy (ΔG) determines spontaneity of reaction.
- ΔG < 0 : Spontaneous reaction
- ΔG = 0 : Reaction at equilibrium
- ΔG > 0 : Non-spontaneous reaction
- Enzymes accelerate reaction rates but do not change equilibrium.
- The energy barrier (transition state) is the highest energy intermediate state of reactants in the conversion to products.
- Enzymes stabilize this state to lower required energy.
Order Reactions
- First-order reactions are directly proportional to reactant concentration.
Michaelis-Menten Kinetics
- Michaelis-Menten equation describes enzyme kinetics.
- kcat (turnover number) is the number of substrate molecules converted to product per enzyme molecule per second.
- kcat / Km is the catalytic efficiency of the enzyme.
- Km is the substrate concentration at which the reaction rate is half of the maximum rate (Vmax).
- Vmax is the maximum reaction rate.
Allosteric Regulation
- Allosteric regulation is where a regulatory molecule binds to an enzyme at a non-active site (allosteric site). This affects enzyme activity.
- Allosteric inhibitors change the active site to work less well.
- Allosteric activators bind to sites other than the active site, improving the function of the active site.
- Cooperativity describes how the binding of one substrate molecule affects the binding of subsequent substrates to the active site.
Enzyme Inhibition
- Competitive inhibition: Inhibitor competes with substrate for the active site, increasing km, but not affecting vmax.
- Non-competitive inhibition: Inhibitor binds to a site other than the active site, decreasing Vmax but not affecting km..
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Description
Explore the fascinating world of enzymes in this quiz. Learn about how these remarkable catalysts speed up biochemical reactions, their specific structure, and the crucial role of cofactors. Challenge your understanding of enzyme specificity, active sites, and the different models of enzyme action.
