Chemistry: First-Order Reaction and Enzyme Catalysis
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Questions and Answers

What is the relationship between the initial velocity Vo and the substrate concentration [S] in enzyme catalysis?

  • Vo is independent of [S]
  • Vo is proportional to [S]²
  • Vo is inversely proportional to [S]
  • Vo is directly proportional to [S] (correct)

    • What is the role of the enzyme in the Michaelis-Menten equation?

  • To decrease the substrate concentration [S]
  • To bind to the substrate and form an enzyme-substrate complex (correct)
  • To increase the substrate concentration [S]
  • To break the substrate into product

    • What is the significance of the Michaelis-Menten constant KM?

  • It is the concentration of the substrate at which the enzyme is half-saturated (correct)
  • It is the rate constant for the binding of the substrate to the enzyme
  • It is the rate constant for the catalysis of the substrate to the product
  • It is the concentration of the product at which the enzyme is fully saturated

    • What is the assumption of the Michaelis-Menten equation?

    <p>The substrate concentration [S] is much greater than the enzyme concentration [E]</p> Signup and view all the answers

    What is the relationship between the maximum velocity Vmax and the initial velocity Vo?

    <p>Vmax is equal to Vo</p> Signup and view all the answers

    What is the purpose of the formation of the enzyme-substrate complex in enzyme catalysis?

    <p>To facilitate the binding of the substrate to the enzyme</p> Signup and view all the answers

    What is the rate-determining step in enzyme catalysis?

    <p>The formation of the transition state</p> Signup and view all the answers

    What is the effect of increasing the substrate concentration [S] on the initial velocity Vo?

    <p>Vo increases initially and then levels off</p> Signup and view all the answers

    What is the study of the rates at which chemical reactions occur?

    <p>Kinetics</p> Signup and view all the answers

    What is the equation for the rate of a reaction with aA + bB → P?

    <p>Rate = k[A]a[B]b</p> Signup and view all the answers

    What is the order of a reaction with rate equation Rate = k[A]a[B]b?

    <p>a + b</p> Signup and view all the answers

    What is the rate equation for a first-order reaction A → P?

    <p>v = -d[A]/dt = k[A]</p> Signup and view all the answers

    What is the term for the time it takes for the concentration of a reactant to decrease to half of its initial value?

    <p>Half-life</p> Signup and view all the answers

    What is the rate equation for a second-order reaction A + B → P?

    <p>v = k[A][B]</p> Signup and view all the answers

    What is the term for the state in which the reactants and products are in equilibrium?

    <p>Equilibrium</p> Signup and view all the answers

    What is the effect of catalysis on the free energy of activation?

    <p>Decreases the free energy of activation</p> Signup and view all the answers

    What is the effect of increasing [S] on the Vo in the Michaelis-Menten equation?

    <p>Vo increases and approaches Vmax</p> Signup and view all the answers

    What is the purpose of the Lineweaver-Burk plot?

    <p>To determine the KM value</p> Signup and view all the answers

    In competitive inhibition, what is the effect of increasing [I] on the Vo?

    <p>Vo decreases</p> Signup and view all the answers

    What is the equation for the Eadie-Hofstee plot?

    <p>Vo = -KM/[S] + Vmax</p> Signup and view all the answers

    What is the difference between competitive and non-competitive inhibition?

    <p>Competitive inhibition affects KM, while non-competitive inhibition affects Vmax</p> Signup and view all the answers

    What is the purpose of the Michaelis-Menten equation?

    <p>To describe the kinetics of enzyme-catalyzed reactions</p> Signup and view all the answers

    What is the effect of increasing [S] on the Vo at low [S] values?

    <p>Vo increases rapidly</p> Signup and view all the answers

    What is the Km value in the Michaelis-Menten equation?

    <p>The substrate concentration at which Vo is half of Vmax</p> Signup and view all the answers

    Study Notes

    First-Order Reaction

    • V = kF[S] – kB[P]
    • kF[S] = kB[P] at equilibrium
    • Vo = kF[S]
    • Initial velocity (Vo) is proportional to substrate concentration [S]

    Enzyme Catalysis

    • Formation of enzyme-substrate complex: E + S → E—S
    • Binding: k1, k-1; Catalysis: k2
    • Vo = k2[ES]

    Michaelis-Menten Formulation

    • Formation of enzyme-substrate complex: E + S → E—S
    • Transition state: E—S* → E + P
    • Michaelis-Menten equation: Vo = k+2[E]A[S] / (KM + [S])
    • [EA] = total active enzyme molecules
    • Vmax = k2[E]A

    Enzyme Kinetics

    • Progress curves: steady-state
    • Lineweaver-Burk plot: 1/Vo = 1/Vmax + KM/Vmax[1/[S]]
    • Eadie-Hofstee plot: Vo = -KM/Vmax[1/[S]] + Vmax

    Inhibition

    • Competitive inhibitor: E + I → E—I (inactive)
    • Non-competitive inhibitor: E + S → E—S; E—I (inactive)
    • Competitive inhibitor plots: 1/Vo = 1/Vmax + KI/Vmax[1/[S]]
    • Non-competitive inhibitor plots: Vo = -KM/Vmax[1/[S]] + Vmax

    Chemical Kinetics

    • Definition: study of rates of chemical reactions
    • Elementary reactions: A → P
    • Rate equations: Rate = k[A]a[B]b (a + b = order of reaction)
    • Molecularity of reaction: first-order, second-order, etc.

    Rate Equations

    • First-order reaction: v = -d[A]/dt = k[A]
    • Second-order reaction: v = -d[A]/dt = k[A][B]

    Transition State

    • Definition: high-energy state during chemical reaction
    • Example: CH3Br + OH- → CH3OH + Br-

    Thermodynamics of the Transition State

    • Two-step reactions: k1, k2
    • Rate-determining step: the slowest step determines the overall rate

    Accelerating Chemical Reactions

    • Heat: increases kinetic energy of molecules
    • pH: affects reaction rates
    • Catalysis: reduces ∆G‡, increasing reaction rates

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    Description

    This quiz covers the concepts of first-order reaction, enzyme catalysis, and the Michaelis-Menten formulation. It includes the kinetics of substrate-enzyme interactions and the calculation of initial velocity.

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