Biochem 5.2 Enzyme Kinetics Quiz
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Questions and Answers

What happens to the enzyme's active sites as substrate concentration approaches infinity?

  • They become fully bound to substrate. (correct)
  • They remain unoccupied.
  • They become inactive.
  • They can no longer bind to substrate.

How is the affinity of an enzyme for its substrate indicated by the KM value?

  • A large KM indicates high affinity.
  • A small KM indicates high affinity. (correct)
  • A small KM indicates low affinity.
  • KM has no relation to affinity.

What is true about Vmax in relation to enzyme concentration?

  • Vmax is the same regardless of experimental conditions.
  • An increase in enzyme concentration results in a higher Vmax. (correct)
  • Vmax is achieved without substrate saturation.
  • Vmax is independent of enzyme concentration.

When can Vmax be achieved?

<p>When the enzyme is saturated with substrate. (D)</p> Signup and view all the answers

What does a large KM value indicate about an enzyme's interaction with its substrate?

<p>It binds the substrate weakly. (A), It requires a larger substrate concentration to reach half-maximal velocity. (C)</p> Signup and view all the answers

What is the significance of the turnover number (kcat) in enzyme kinetics?

<p>It is an intensive property representing the enzyme's activity. (D)</p> Signup and view all the answers

Which of the following statements about KM is correct?

<p>KM can be used for enzymes that do not follow Michaelis-Menten kinetics. (D)</p> Signup and view all the answers

What is required for an enzyme to operate at Vmax during experiments?

<p>The enzyme must be saturated with substrate. (C)</p> Signup and view all the answers

What does an enzyme's Vmax indicate?

<p>The maximum rate of reaction under specific conditions. (D)</p> Signup and view all the answers

What does the Michaelis constant (KM) help describe about an enzyme?

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

At what substrate concentration ([S]) does the reaction proceed at half-maximal velocity (½Vmax)?

<p>[S] = KM (D)</p> Signup and view all the answers

If [S] is equal to 2KM, what fraction of the total enzyme is bound to substrate?

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

Which variable is independent in the Michaelis-Menten equation?

<p>[S] (D)</p> Signup and view all the answers

When analyzing an enzyme's catalytic efficiency, which two parameters are combined to form a new constant?

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

What unit is used for both Kd and KM constants?

<p>Concentration (e.g., mM) (B)</p> Signup and view all the answers

If the substrate concentration [S] is equal to nKM, how is V0 represented as a function of Vmax?

<p>$V_0 = \frac{n}{1 + n} V_{max}$ (B)</p> Signup and view all the answers

What does a lower KM value indicate about the enzyme's affinity for its substrate?

<p>Higher affinity for the substrate (C)</p> Signup and view all the answers

If all enzymes in a solution are bound to substrate, what can be inferred about the substrate concentration?

<p>[S] is significantly greater than KM (C)</p> Signup and view all the answers

What does the turnover number (kcat) represent?

<p>The number of reactions catalyzed per enzyme per unit time (B)</p> Signup and view all the answers

How is kcat related to Vmax and total enzyme concentration?

<p>kcat equals Vmax divided by total enzyme concentration (B)</p> Signup and view all the answers

What units does kcat possess?

<p>Reciprocal time, such as min−1 or s−1 (B)</p> Signup and view all the answers

How does an increase in kcat affect an enzyme's catalytic efficiency?

<p>Catalytic efficiency increases (A)</p> Signup and view all the answers

What does the Michaelis constant (KM) indicate?

<p>The enzyme’s affinity for its substrate (B)</p> Signup and view all the answers

What is catalytic efficiency also known as?

<p>Specificity constant (D)</p> Signup and view all the answers

How are kcat and KM combined to indicate enzyme effectiveness?

<p>By dividing kcat by KM (A)</p> Signup and view all the answers

What effect does a decrease in KM have on catalytic efficiency?

<p>Catalytic efficiency increases (D)</p> Signup and view all the answers

What happens when all enzyme molecules are saturated with substrate?

<p>Vmax is reached (C)</p> Signup and view all the answers

Which of the following equations represents the relationship between Vmax, kcat, and Etot?

<p>Vmax = kcat * [Etot] (A)</p> Signup and view all the answers

Flashcards

What is the Michaelis constant (KM)?

The Michaelis constant (KM) is a measure of an enzyme's affinity for its substrate. It represents the substrate concentration at which the reaction rate is half its maximum value (Vmax).

What happens when [S] = KM?

When the substrate concentration ([S]) is equal to the KM value, the reaction proceeds at half the maximum velocity (Vmax).

How does KM relate to enzyme-substrate affinity?

The KM value provides insight into an enzyme's affinity for its substrate. A lower KM indicates a higher affinity, meaning the enzyme can achieve half-maximal velocity at a lower substrate concentration.

What is the Michaelis-Menten equation?

The Michaelis-Menten equation describes the relationship between reaction rate (V0) and substrate concentration ([S]) for an enzyme-catalyzed reaction. It includes the parameters Vmax and KM.

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What is Vmax?

Vmax represents the maximum reaction velocity that can be achieved by an enzyme under saturating substrate conditions. It is reached when all enzyme molecules are bound to substrate.

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What is the catalytic rate constant (kcat)?

The catalytic rate constant (kcat) describes the turnover number, or the number of substrate molecules converted to product per unit time by a single enzyme molecule.

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What is catalytic efficiency?

Catalytic efficiency is a measure of how efficiently an enzyme converts substrate to product. It is calculated by kcat/KM, reflecting the rate constant for the conversion of substrate to product under conditions where the substrate concentration is much lower than KM.

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What does a high kcat/KM value tell us?

A high kcat/KM value indicates that an enzyme binds to its substrate with high affinity (low KM) and converts it to product at a rapid rate (high kcat).

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How does KM relate to the dissociation constant (Kd)?

The KM value is not a true binding constant but can be used to describe the affinity of an enzyme for its substrate. Kd, on the other hand, is a true binding constant that represents the dissociation constant.

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What are the Michaelis-Menten parameters?

The Michaelis-Menten parameters (Vmax and KM) are constants within an experiment, meaning they remain unchanged under the same set of conditions.

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What is the relationship between KM and affinity?

The enzyme's affinity for its substrate is inversely proportional to the KM value.

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What does a small KM value indicate?

A small KM value indicates a high affinity for the substrate, meaning it takes a small concentration of substrate to reach half-maximal velocity.

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What does a large KM value indicate?

A large KM value indicates a low affinity for the substrate, meaning it takes a large concentration of substrate to reach half-maximal velocity.

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What is kcat (turnover number)?

The number of substrate molecules that one molecule of enzyme can convert to product per unit time when the enzyme is saturated.

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Why is kcat important?

It is the enzyme's intrinsic property, independent of the enzyme concentration used in the experiment.

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How does enzyme concentration affect Vmax?

Vmax depends on the amount of enzyme used in the experiment. More enzyme means a higher Vmax.

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How is kcat calculated?

By dividing Vmax by the enzyme concentration, kcat can be calculated.

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Why are KM and kcat important for understanding enzyme kinetics?

It provides valuable information about the enzyme's catalytic efficiency and affinity for its substrate.

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Turnover Number (kcat)

The number of substrate molecules an enzyme can convert to product per unit time when the enzyme is saturated with substrate.

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Catalytic Efficiency (kcat/KM)

A measure of how efficiently an enzyme converts substrate to product. It is calculated by dividing the enzyme's kcat value by its KM value.

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Study Notes

Michaelis-Menten Parameters

  • Michaelis-Menten equation involves variables V₀ and [S], and constants Vmax and KM.

  • Vmax relates to the catalytic rate constant kcat.

  • KM has units of concentration (e.g., mM).

  • KM describes enzyme affinity for its substrate

  • If [S] = KM, reaction proceeds at half-maximal velocity (½Vmax).

  • V₀ = (Vmax * [S]) / (KM + [S])

  • V0,[S]=KM = Vmax / 2

  • Vo as a percentage of Vmax can be estimated using [S] as multiple (n) of KM

  • n * KM / (KM + n * KM) * Vmax = Vo = (n / (n + 1)) * Vmax

Turnover Number (kcat) and Maximum Reaction Velocity (Vmax)

  • Vmax: Maximal reaction velocity; achieved when enzyme is saturated with substrate
  • Vmax measures product concentration per unit time (e.g., µM / min)
  • kcat: Turnover number; describes substrate molecules converted to products per unit time at saturation

Catalytic Efficiency (kcat / KM)

  • Catalytic efficiency combines KM and kcat into a single constant (specificity constant)
  • Higher kcat (more rapid conversion at saturation), and lower KM (higher affinity) increase efficiency
  • Efficiency is an indication of how well an enzyme catalyzes its reaction
  • A high catalytic efficiency value (10⁸ M⁻¹s⁻¹) implies a very rapid rate of reaction. The enzyme is considered "catalytically perfect."

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Biochemistry 5.2 Michaelis-Menten Parameters PDF

Description

Test your understanding of enzyme kinetics with this quiz. Explore concepts such as Vmax, KM, and the turnover number (kcat) in enzymes. Learn how affinity and substrate concentration affect enzyme activity.

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