Q: Which of the following enzymes has the highest catalytic efficiency, as measured by $k_{cat}/K_M$?

Acetylcholinesterase with $k_{cat} = 1.4 \times 10^4$ s$^{-1}$ and $K_M = 9.0 \times 10^{-5}$ M

Question 1

Which of the following best describes the meaning of $K_M$ in the Michaelis-Menten equation?

Accepted Answer

The substrate concentration at which the initial velocity $v_0$ is half of $V_{max}$.

Question 2

An enzyme has a $K_M$ of 0.05 mM for glucose and 1.5 mM for fructose. What does this indicate about the enzyme’s affinity for these substrates?

Accepted Answer

The enzyme has higher affinity for glucose than fructose.

Question 3

Which equation correctly represents the Michaelis-Menten relationship between initial velocity $v_0$ and substrate concentration $[S]$?

Accepted Answer

$v_0 = \frac{V_{max}[S]}{K_M + [S]}$

Question 4

If an enzyme operates under steady-state conditions, which of the following is true?

Accepted Answer

The concentration of ES complex remains constant over time.

Question 5

What is the turnover number ($k_{cat}$) of an enzyme?

Accepted Answer

The number of substrate molecules converted to product per enzyme molecule per unit time.

Question 6

Which of the following enzymes has the highest catalytic efficiency, as measured by $k_{cat}/K_M$?

Accepted Answer

Acetylcholinesterase with $k_{cat} = 1.4 	imes 10^4$ s$^{-1}$ and $K_M = 9.0 	imes 10^{-5}$ M

Question 7

Which of the following is the correct Lineweaver-Burk equation derived from the Michaelis-Menten equation?

Accepted Answer

$\frac{1}{v_0} = \frac{K_M}{V_{max}[S]} + \frac{1}{V_{max}}$

Question 8

A researcher measures the initial velocity $v_0$ of an enzyme-catalyzed reaction at various substrate concentrations. She finds that doubling $[S]$ does not double $v_0$. What is the most likely explanation?

Accepted Answer

The enzyme is saturated with substrate and operating near $V_{max}$.

Question 9

Which of the following statements about $V_{max}$ is correct?

Accepted Answer

$V_{max}$ is reached when all enzyme molecules are bound to substrate.

Question 10

In a single-step enzyme mechanism, which rate constant is equivalent to $k_{cat}$?

Accepted Answer

$k_2$

Question 11

If $k_2 \ll k_{-1}$ in the Michaelis-Menten mechanism, what does $K_M$ approximate?

Accepted Answer

$K_M \approx K_D = \frac{k_{-1}}{k_1}$

Question 12

Which of the following best describes the specificity constant ($k_{cat}/K_M$)?

Accepted Answer

It is a second-order rate constant for the conversion of E + S to E + P.

Question 13

A mutation in an enzyme increases $K_M$ but does not affect $V_{max}$. What is the most likely effect on enzyme function?

Accepted Answer

The enzyme will require a higher substrate concentration to reach half-maximal velocity.

Question 14

Which of the following is true about the initial velocity ($v_0$) in Michaelis-Menten kinetics?

Accepted Answer

It is measured before significant product has accumulated.

Question 15

Which graphical method allows for easy determination of $K_M$ and $V_{max}$ from experimental data?

Accepted Answer

Lineweaver-Burk double-reciprocal plot

Question 16

If an enzyme’s $k_{cat}/K_M$ approaches $10^8$ to $10^9$ M$^{-1}$s$^{-1}$, what does this indicate?

Accepted Answer

The enzyme is operating at the diffusion-controlled limit.

Question 17

Which of the following is a correct interpretation of the y-intercept in a Lineweaver-Burk plot?

Accepted Answer

It equals $1/V_{max}$.

Question 18

A patient has a genetic mutation that reduces the $k_{cat}$ of an important metabolic enzyme. What is the most likely physiological consequence?

Accepted Answer

Slower conversion of substrate to product, potentially leading to metabolic buildup.

Question 19

Which of the following is true regarding the steady-state assumption in enzyme kinetics?

Accepted Answer

The rate of formation of ES equals the rate of its consumption.

Enzyme Kinetics and the Michaelis-Menten Equation: Structured Study Notes

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