Enzyme Kinetics and Inhibition
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Questions and Answers

What does Kcat represent in enzyme kinetics?

  • The maximum rate at which an enzyme can convert substrate to product
  • The affinity of an enzyme for its substrate
  • The concentration of free enzyme at steady state
  • The rate of ES complex formation per unit time (correct)

    • What is indicated by the term 'steady state' in enzyme kinetics?

  • The rate of formation and breakdown of the ES complex balances out (correct)
  • The concentration of the substrate remains constant over time
  • The enzyme concentration varies throughout the reaction
  • The substrate is fully consumed by the enzyme

    • Which assumption must be met for Michaelis-Menten kinetics to apply?

  • The enzyme concentration needs to be greater than the substrate concentration
  • The reaction reaches its final product before measuring initial rates
  • The enzyme concentration must be less than the substrate concentration (correct)
  • All substrate must bind to the enzyme simultaneously

    • What does the term Km measure in the context of enzyme kinetics?

    <p>The affinity of the enzyme for its substrate</p> Signup and view all the answers

    How is Vmax affected in enzymatic reactions?

    <p>It depends on the concentration of the enzyme</p> Signup and view all the answers

    What is the Vmax for the uninhibited enzyme as given?

    <p>25 mM/s</p> Signup and view all the answers

    What is the value of Km for the uninhibited enzyme?

    <p>0.09 mg/mL</p> Signup and view all the answers

    If 10 nmol of enzyme is used in a 100 μL reaction, which formula helps in calculating kcat?

    <p>kcat = Vmax / [E]</p> Signup and view all the answers

    In the provided content, what is the reaction volume stated for the enzyme activity?

    <p>100 μL</p> Signup and view all the answers

    What is the first step to find kcat as mentioned in the content?

    <p>Calculate Umax</p> Signup and view all the answers

    How is Km represented in the context provided?

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

    What unit is used to express the Vmax in the provided content?

    <p>mM/s</p> Signup and view all the answers

    What is the concentration of the enzyme in the solution if 10 nmol of enzyme is used in a 100 μL reaction?

    <p>1 μM</p> Signup and view all the answers

    What process do proteases use to cleave proteins?

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

    Which of the following best describes hydrolysis in the context of proteases?

    <p>Exergonic and energy-releasing</p> Signup and view all the answers

    What is a key characteristic of the catalytic trend in serine proteases?

    <p>They cleave peptide bonds through acylation-deacylation</p> Signup and view all the answers

    What are the primary roles of nucleophiles and electrophiles during the reaction with proteases?

    <p>Nucleophiles attack electrophiles to facilitate bond cleavage</p> Signup and view all the answers

    Which amino acid residues are commonly involved in the catalytic mechanism of serine proteases?

    <p>Asp-His-Ser</p> Signup and view all the answers

    What type of kinetics is exhibited by chymotrypsin?

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

    What is the effect of a catalyst on the rate of a reaction involving hydrolysis by proteases?

    <p>Accelerates the reaction rate</p> Signup and view all the answers

    In the context of proteolysis, what does the term 'acyl-enzyme' refer to?

    <p>A transient intermediate in the reaction</p> Signup and view all the answers

    What does the variable kat represent in the context provided?

    <p>Rate of turnover</p> Signup and view all the answers

    What is the unit for the slope calculated in the content?

    <p>nm/min</p> Signup and view all the answers

    At what concentration is Kat calculated to be 60,600 min?

    <p>6.06 x 10^-3 M</p> Signup and view all the answers

    What does Vmax represent in the equations provided?

    <p>Maximum turnover rate</p> Signup and view all the answers

    What is the relation of kat to [C]T and [E]T in the equation for Vmax?

    <p>Vmax = kat * [E]T</p> Signup and view all the answers

    How is specificity constant calculated according to the given information?

    <p>kat divided by [C]</p> Signup and view all the answers

    What does the term 0.0606 x 10^-3 M/m denote?

    <p>Kat value</p> Signup and view all the answers

    Which of the following denotes a concentration conversion mentioned in the content?

    <p>1 mm = 10^3 nm</p> Signup and view all the answers

    What happens to enzyme activity when temperature increases?

    <p>Enzyme activity initially increases and then stabilizes.</p> Signup and view all the answers

    What is the effect of competitive inhibitors on enzyme activity?

    <p>They bind to the active site, preventing substrate binding.</p> Signup and view all the answers

    What is the effect of uncompetitive inhibitors on Km and Vmax?

    <p>Both Km and Vmax decrease.</p> Signup and view all the answers

    Which type of inhibitor binds equally to the enzyme regardless of substrate presence?

    <p>Noncompetitive inhibitor</p> Signup and view all the answers

    What is observed in a double-reciprocal plot when a competitive inhibitor is present?

    <p>The slope increases while the y-intercept remains the same.</p> Signup and view all the answers

    What is the effect of noncompetitive inhibitors on Vmax?

    <p>Vmax decreases but Km remains unchanged.</p> Signup and view all the answers

    How do irreversible inhibitors typically affect enzymes?

    <p>They permanently attach to the enzyme.</p> Signup and view all the answers

    What is the typical impact of a competitive inhibitor on the Km value?

    <p>Km increases.</p> Signup and view all the answers

    What characteristic is unique to uncompetitive inhibitors compared to competitive inhibitors?

    <p>They decrease both Km and Vmax.</p> Signup and view all the answers

    What does a higher Km value indicate about an enzyme's affinity for a substrate?

    <p>Lower affinity for the substrate.</p> Signup and view all the answers

    Which type of inhibition occurs when an inhibitor binds to a site other than the active site?

    <p>Noncompetitive inhibition</p> Signup and view all the answers

    What changes occur in the presence of a competitive inhibitor according to the Michaelis-Menten kinetics?

    <p>Km increases while Vmax remains constant.</p> Signup and view all the answers

    What is indicated by a decrease in Vmax when an enzyme is inhibited?

    <p>The enzyme's overall activity has decreased.</p> Signup and view all the answers

    Which of the following describes the behavior of noncompetitive inhibitors?

    <p>They do not affect substrate binding.</p> Signup and view all the answers

    Study Notes

    Uninhibited Enzyme

    • The uninhibited enzyme's Vmax is 25 mM/s.
    • The uninhibited enzyme's Km is 0.09 mg/mL.

    Kcat Calculation

    • The enzyme concentration is 10 nmol in a 100 μL reaction.
    • The Kcat is calculated using the formula: Kcat = Vmax / [ET].
    • The Kcat is 60,600 min.

    Enzyme Kinetics

    • Km is a measure of substrate affinity, representing the substrate's binding to the enzyme.
    • Vmax is a measure of enzyme rate, dependent on enzyme concentration.

    Enzyme Activity and Temperature

    • Increased temperature initially increases enzyme rate, as it increases the stability of the protein/enzyme.

    Enzyme Activity and Protonation/Deprotonation

    • Enzyme activity depends on the protonation/deprotonation of specific groups, which can activate or deactivate the enzyme.

    Inhibitors

    • Competitive inhibitors bind to the active site, preventing substrate binding.
    • Uncompetitive inhibitors bind to the enzyme-substrate complex, preventing product formation.
    • Noncompetitive inhibitors bind to an allosteric site, affecting enzyme conformation and activity.

    Double-Reciprocal Plot

    • Double-reciprocal plots (Lineweaver-Burk plots) are used to represent enzyme kinetic data linearly.
    • Competitive, uncompetitive, and noncompetitive inhibition can be distinguished by analyzing the changes in slope and y-intercept of the plot.

    Irreversible Inhibitors

    • Irreversible inhibitors typically form a covalent bond with the enzyme, permanently inactivating it.

    Protease Kinetics

    • Proteases cleave proteins by hydrolysis.
    • Chymotrypsin demonstrates biphasic kinetics due to its acylation-deacylation mechanism.

    Serine Protease Kinetics

    • Serine proteases have an Asp-His-Ser catalytic triad.
    • Kinetics follow a specific rate equation with specific Km and Vmax values.
    • The Kcat for serine protease is 60,600 min.
    • Specificity constant (Kcat/Km) is a measure of the enzyme's preference for a particular substrate.

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    Exam 2 PDF - Chapter 6 Enzymes

    Description

    This quiz covers the fundamentals of enzyme kinetics, including concepts such as Vmax, Km, Kcat, and the effects of temperature on enzyme activity. It also explores the mechanisms of enzyme inhibition, differentiating between competitive and uncompetitive inhibitors. Test your understanding of how these factors impact enzyme functionality.

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