Question 1

Which of the following best describes a first-order reaction in biochemistry?

Accepted Answer

A reaction where the rate is directly proportional to the concentration of a single reactant.

Question 2

What are the units of the rate constant for a second-order (bimolecular) reaction?

Accepted Answer

$\mathrm{M}^{-1}\mathrm{s}^{-1}$

Question 3

According to the Michaelis-Menten model, which equation correctly describes the initial velocity $V_0$ of an enzyme-catalyzed reaction?

Accepted Answer

$V_0 = V_{max} \dfrac{[S]}{[S] + K_M}$

Question 4

What does the Michaelis constant $K_M$ represent in enzyme kinetics?

Accepted Answer

The substrate concentration at which the reaction velocity is half of $V_{max}$.

Question 5

Which of the following is the correct formula for the Michaelis constant $K_M$ in terms of rate constants?

Accepted Answer

$K_M = \dfrac{k_{-1} + k_2}{k_1}$

Question 6

In the context of enzyme kinetics, what does the turnover number ($k_{cat}$) indicate?

Accepted Answer

The number of substrate molecules converted to product per unit time at a single catalytic site when the enzyme is fully saturated.

Question 7

Which of the following statements about allosteric enzymes is TRUE?

Accepted Answer

They have multiple active sites and display cooperativity, often showing a sigmoidal dependence of reaction velocity on substrate concentration.

Question 8

A Lineweaver-Burk plot is used to analyze enzyme kinetics. What do the x-axis and y-axis represent?

Accepted Answer

x-axis: $1/[S]$, y-axis: $1/V_0$

Question 9

If an inhibitor causes $V_{max}$ to decrease but does not change $K_M$, what type of inhibition is most likely occurring?

Accepted Answer

Uncompetitive inhibition

Question 10

Which of the following best describes the steady-state assumption in enzyme kinetics?

Accepted Answer

The concentration of the enzyme-substrate complex remains constant even as substrate and product concentrations change.

Question 11

Cystathioninuria is a rare condition caused by a deficiency in which enzyme, and what coenzyme does it require?

Accepted Answer

Cystathionase; pyridoxal phosphate (Vitamin B$_6$)

Question 12

Which of the following is a correct interpretation of the Michaelis-Menten equation when $[S] \gg K_M$?

Accepted Answer

The reaction velocity approaches $V_{max}$.

Question 13

In a metabolic pathway, which enzyme is most likely to be allosteric and regulate the pathway?

Accepted Answer

The enzyme catalyzing the committed, irreversible step.

Question 14

Single-molecule enzyme studies are important because they:

Accepted Answer

Reveal a distribution of enzyme characteristics that cannot be obtained from ensemble methods.

Question 15

Which of the following equations gives the concentration of the enzyme-substrate complex $[ES]$ in terms of total enzyme concentration $[E]_T$, substrate concentration $[S]$, and $K_M$?

Accepted Answer

$[ES] = \dfrac{[E]_T [S]}{[S] + K_M}$

Question 16

A patient with cystathioninuria is given Vitamin B$_6$ supplements and shows restored enzyme activity. What is the most likely molecular explanation?

Accepted Answer

The mutation decreases the affinity for the coenzyme pyridoxal phosphate, so higher concentrations restore activity.

Question 17

Which ratio is commonly used to assess enzyme efficiency?

Accepted Answer

$k_{cat} / K_M$

Question 18

If the concentration of substrate $[S]$ is much lower than $K_M$, how does the initial velocity $V_0$ depend on $[S]$?

Accepted Answer

$V_0$ increases linearly with $[S]$

Question 19

Which of the following is a potential danger when correlating enzyme absence with a pathological condition, as illustrated by cystathioninuria?

Accepted Answer

Assuming causation from a small sample size can lead to erroneous conclusions.

Biochemistry: A Short Course 7

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