Enzyme Catalyzed Reactions and Michaelis-Menten

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Questions and Answers

What does the symbol $K_M$ represent in the Michaelis-Menten equation?

  • Time taken for the reaction to complete
  • Substrate concentration at half-maximal velocity (correct)
  • Maximum substrate concentration
  • Rate constant for the enzyme-substrate complex

In the reaction mechanism, what does the symbol ES represent?

  • Enzyme-State complex
  • Enzyme-Substrate complex (correct)
  • Enzyme-Specificity complex
  • Enzyme-Product complex

What happens to the reaction velocity as substrate concentration increases?

  • It fluctuates randomly
  • It increases linearly without bound
  • It decreases exponentially
  • It becomes constant at $V_{max}$ (correct)

A high value of $K_M$ indicates what about the enzyme’s affinity for the substrate?

<p>Low affinity for the substrate (D)</p> Signup and view all the answers

Which rate constant corresponds to the formation of the product from the enzyme-substrate complex?

<p>$k_{cat}$ (C)</p> Signup and view all the answers

What does a low value of $K_M$ signify about an enzyme's catalytic activity?

<p>It suggests high enzyme affinity for the substrate (C)</p> Signup and view all the answers

What does the Michaelis-Menten equation help to describe?

<p>The relationship between reaction velocity and substrate concentration (B)</p> Signup and view all the answers

What does the symbol 'E' represent in the enzyme catalyzed reaction?

<p>Enzyme (C)</p> Signup and view all the answers

In the steady-state assumption, what happens to the enzyme-substrate complex (ES)?

<p>It is formed as quickly as it breaks down. (A)</p> Signup and view all the answers

What does the Michaelis-Menten constant (Km) signify?

<p>The substrate concentration at ½ Vmax. (B)</p> Signup and view all the answers

Which statement correctly describes the velocity of the reaction at high substrate concentrations?

<p>Velocity approaches Vmax. (C)</p> Signup and view all the answers

Which rate constant in the enzyme reaction limits the overall reaction rate?

<p>kcat (B)</p> Signup and view all the answers

What does the Michaelis-Menten equation express?

<p>The relationship between reaction velocity and substrate concentration. (C)</p> Signup and view all the answers

Which of the following statements about substrate concentration and reaction rate at low concentrations is true?

<p>Reaction rate is directly proportional to substrate concentration. (A)</p> Signup and view all the answers

In the equation $K_m = \frac{k_{-1} + k_{cat}}{k_1}$, what does the numerator represent?

<p>The total rate of enzyme-substrate complex breakdown. (A)</p> Signup and view all the answers

What occurs when more active sites are occupied in an enzyme-catalyzed reaction?

<p>The reaction rate drops off as saturation occurs. (A)</p> Signup and view all the answers

What do the symbols $k_{1}$, $k_{2}$, and $k_{3}$ represent in the enzyme-catalyzed reaction?

<p>The rates of the reaction steps (C)</p> Signup and view all the answers

Which statement accurately describes the steady state in an enzyme-catalyzed reaction?

<p>The concentration of ES remains approximately constant. (B)</p> Signup and view all the answers

What occurs during the pre-steady state of an enzyme-catalyzed reaction?

<p>The concentration of ES increases and changes. (D)</p> Signup and view all the answers

Which component of the enzyme-catalyzed reaction is released unchanged?

<p>Enzyme (E) (C)</p> Signup and view all the answers

Which graph characteristic indicates the steady state during the enzyme-catalyzed reaction?

<p>The concentration of product plateaus. (A)</p> Signup and view all the answers

How does the rate of the overall reaction relate to the breakdown of the ES complex?

<p>The rate is limited by the slower breakdown of the ES complex. (C)</p> Signup and view all the answers

What happens to the concentration of the enzyme-substrate complex (ES) at steady state?

<p>It remains approximately constant. (D)</p> Signup and view all the answers

What role does the substrate (S) play in the enzyme-catalyzed reaction?

<p>It is the molecule that the enzyme acts upon. (B)</p> Signup and view all the answers

What happens to the enzyme concentration ([E]) during the enzyme-catalyzed reaction?

<p>It remains relatively constant during the reaction. (D)</p> Signup and view all the answers

Flashcards

Michaelis-Menten Equation

Equation describing the relationship between reaction velocity (v) and substrate concentration ([S]) in an enzyme-catalyzed reaction.

Vmax

Maximum velocity of an enzyme-catalyzed reaction; the theoretical fastest rate.

KM

Michaelis constant; substrate concentration at which the reaction velocity is half of Vmax. Shows how well the enzyme binds to a substrate.

High KM

Low affinity of the enzyme for the substrate; need high substrate concentration for half maximal reaction velocity.

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Low KM

High affinity of the enzyme for the substrate; low substrate concentration for half maximal reaction velocity.

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Enzyme-Substrate Complex (ES)

Intermediate formed when an enzyme binds to its substrate.

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Reaction Velocity (v)

The rate at which a reaction proceeds in an enzyme-catalyzed reaction.

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Enzyme-catalyzed reaction

A reaction where an enzyme speeds up the conversion of a substrate into a product

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Steady-state assumption

In an enzymatic reaction, the rate of formation of the enzyme-substrate complex is equal to its breakdown rate.

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Michaelis-Menten constant

A constant that represents the substrate concentration at which the reaction rate is half of the maximum reaction velocity.

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Pre-steady state

The initial phase of an enzyme reaction where the ES concentration changes dynamically.

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Steady state

The phase of an enzyme reaction where the ES concentration is approximately constant.

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Substrate (S)

The molecule that the enzyme acts upon.

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Product (P)

The molecule produced during the enzyme-catalyzed reaction.

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Enzyme (E)

A biological catalyst that speeds up chemical reactions.

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Michaelis-Menten constant (Km)

A measure of the substrate concentration required for an enzyme to reach half its maximum velocity (Vmax).

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What is the Michaelis-Menten equation?

V = (Vmax * [S]) / (Km + [S]) Where V is the reaction velocity, Vmax is the maximum velocity, [S] is the substrate concentration, and Km is the Michaelis-Menten constant.

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Why is the kcat value important?

The value of kcat determines the maximum rate of product formation, as it represents the turnover number of the enzyme. A higher kcat means a faster reaction rate.

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Study Notes

Enzyme Catalyzed Reaction

  • Enzyme (E) and substrate (S) interact to form an enzyme-substrate complex (ES)
  • The ES complex breaks down to yield the product (P) and the free enzyme (E)
  • The reaction occurs in a series of steps which can occur at different rates
  • The slowest step determines the overall reaction rate
  • The ES complex is formed rapidly compared to its breakdown
  • The slower second reaction must limit the rate of the overall reaction

Michaelis-Menten Equation

  • Describes the velocity of an enzymatic reaction
  • At saturation, velocity (v) = maximum velocity (Vmax)
  • Km = Michaelis-Menten constant
  • Km = [S] at ½ Vmax
  • A high Km means the enzyme has a low affinity for the substrate
  • A low Km means the enzyme has a high affinity for the substrate

Graph

  • The graph shows the relationship between reaction velocity and substrate concentration
  • The curve starts slow and gradually increases then plateaus
  • The curve approaches a maximum velocity (Vmax) as the substrate concentration increases
  • The Km is the substrate concentration that produces half the maximum velocity

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