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?

When the enzyme is saturated with substrate. Signup and view all the answers

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

It binds the substrate weakly. Signup and view all the answers

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

It is an intensive property representing the enzyme's activity. Signup and view all the answers

Which of the following statements about KM is correct?

KM can be used for enzymes that do not follow Michaelis-Menten kinetics. Signup and view all the answers

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

The enzyme must be saturated with substrate. Signup and view all the answers

What does an enzyme's Vmax indicate?

The maximum rate of reaction under specific conditions. Signup and view all the answers

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

The affinity of the enzyme for its substrate Signup and view all the answers

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

[S] = KM Signup and view all the answers

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

Two thirds Signup and view all the answers

Which variable is independent in the Michaelis-Menten equation?

[S] Signup and view all the answers

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

kcat and KM Signup and view all the answers

What unit is used for both Kd and KM constants?

Concentration (e.g., mM) Signup and view all the answers

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

$V_0 = \frac{n}{1 + n} V_{max}$ Signup and view all the answers

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

Higher affinity for the substrate Signup and view all the answers

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

[S] is significantly greater than KM Signup and view all the answers

What does the turnover number (kcat) represent?

The number of reactions catalyzed per enzyme per unit time Signup and view all the answers

How is kcat related to Vmax and total enzyme concentration?

kcat equals Vmax divided by total enzyme concentration Signup and view all the answers

What units does kcat possess?

Reciprocal time, such as min−1 or s−1 Signup and view all the answers

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

Catalytic efficiency increases Signup and view all the answers

What does the Michaelis constant (KM) indicate?

The enzyme’s affinity for its substrate Signup and view all the answers

What is catalytic efficiency also known as?

Specificity constant Signup and view all the answers

How are kcat and KM combined to indicate enzyme effectiveness?

By dividing kcat by KM Signup and view all the answers

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

Catalytic efficiency increases Signup and view all the answers

What happens when all enzyme molecules are saturated with substrate?

Vmax is reached Signup and view all the answers

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

Vmax = kcat * [Etot] Signup and view all the answers

Study Notes

Michaelis-Menten Parameters

Michaelis-Menten equation involves variables V₀ and [S], and constants Vmax and K_M.
Vmax relates to the catalytic rate constant k_cat.
K_M has units of concentration (e.g., mM).
K_M describes enzyme affinity for its substrate
If [S] = K_M, reaction proceeds at half-maximal velocity (½V_max).
V₀ = (V_max * [S]) / (K_M + [S])
V₀,_[S]=KM = V_max / 2
Vo as a percentage of V_max can be estimated using [S] as multiple (n) of K_M
n * K_M / (K_M + n * K_M) * V_max = Vo = (n / (n + 1)) * V_max

Turnover Number (k_cat) and Maximum Reaction Velocity (V_max)

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

Catalytic Efficiency (k_cat / K_M)

Catalytic efficiency combines K_M and k_cat into a single constant (specificity constant)
Higher k_cat (more rapid conversion at saturation), and lower K_M (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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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.