Question 1

Which of the following best describes the primary function of enzymes in cellular metabolism?

Accepted Answer

Enzymes accelerate the rates of reactions by lowering the activation energy.

Question 2

For a simple first-order reaction $$A \rightarrow P$$, which of the following correctly expresses the velocity ($$V) of $$the reaction?

Accepted Answer

$$V = k[A]$$

Question 3

Which statement about the Michaelis–Menten constant ($$K_{\mathrm{M}}) is $$correct?

Accepted Answer

$$K_{\mathrm{M}} is $$the substrate concentration at which the reaction velocity is half of $$V_{\max}.$$

Question 4

A researcher measures the initial velocity ($$V_0) of an $$enzyme-catalyzed reaction at various substrate concentrations and plots $$1/V_0$ versus 1$$/[S]$$. What is this plot called, and what information can be obtained from its slope?

Accepted Answer

This is a Lineweaver–Burk plot; the slope equals $$K_{\mathrm{M}}/V_{\max}.$$

Question 5

Which of the following is a key assumption of the Michaelis–Menten model of enzyme kinetics?

Accepted Answer

The formation and breakdown of the enzyme–substrate complex reach a steady state.

Question 6

An enzyme has a $$K_{\mathrm{M}} of 2 mM $$and a $$V_{\max} of 100$$ $$ \mu $$mol/min. What is the initial velocity ($$V_0) $$when the substrate concentration $$[S] is 2 mM$$?

Accepted Answer

$$V_0 = 50$$ \ \mu \mathrm{mol/min}$$

Question 7

Which of the following best explains why allosteric enzymes often display sigmoidal (S-shaped) velocity-versus-substrate curves?

Accepted Answer

Allosteric enzymes have multiple subunits and exhibit cooperative substrate binding.

Question 8

A patient with a genetic variant of alcohol dehydrogenase has a much higher $$K_{\mathrm{M}}$$ for ethanol than normal. What is the most likely physiological consequence?

Accepted Answer

The patient will metabolize ethanol less efficiently and may experience prolonged intoxication.

Question 9

Which of the following statements about turnover number ($$k_{\mathrm{cat}}) is $$correct?

Accepted Answer

$$k_{\mathrm{cat}} is $$the number of substrate molecules converted to product per enzyme molecule per unit time when the enzyme is fully saturated.

Question 10

Which of the following is a physiological advantage of allosteric regulation in metabolic pathways?

Accepted Answer

It allows rapid and sensitive control of pathway flux in response to cellular signals.

Question 11

In the concerted model for allostery, what is the effect of increasing substrate concentration on the equilibrium between the T (tense) and R (relaxed) states?

Accepted Answer

Increasing substrate concentration shifts the equilibrium toward the R state.

Question 12

A Lineweaver–Burk plot of an enzyme-catalyzed reaction yields a straight line with a y-intercept of 0.02 min/$$\mu$$mol and a slope of 0.1 mM min/$$\mu$$mol. What are the values of $$V_{\max}$$ and $$K_{\mathrm{M}}$$?

Accepted Answer

$$V_{\max} = 50 \ \mu \mathrm{mol/min}$$, $$K_{\mathrm{M}} = 5 \ \mathrm{mM}$$

Question 13

Which of the following is true regarding the specificity constant ($$k_{\mathrm{cat}}/K_{\mathrm{M}}) of an $$enzyme?

Accepted Answer

It measures the catalytic efficiency of the enzyme at low substrate concentrations.

Question 14

Which of the following best describes the effect of a positive allosteric effector on an allosteric enzyme?

Accepted Answer

It binds to the enzyme and stabilizes the R (relaxed) state, lowering the threshold for activity.

Question 15

A metabolic pathway is regulated by feedback inhibition. Which enzyme in the pathway is most likely to be allosterically regulated?

Accepted Answer

The enzyme catalyzing the committed step of the pathway.

Question 16

Which of the following scenarios would most likely result in a sigmoidal (S-shaped) velocity versus substrate concentration curve?

Accepted Answer

An enzyme with multiple subunits and cooperative substrate binding.

Question 17

If an enzyme-catalyzed reaction is measured at substrate concentrations much greater than $$K_{\mathrm{M}}$$, what is the expected effect on the reaction velocity?

Accepted Answer

The reaction velocity will approach $$V_{\max}$$ and become independent of substrate concentration.

Question 18

Which of the following is a characteristic of enzymes that follow Michaelis–Menten kinetics?

Accepted Answer

They display a hyperbolic relationship between velocity and substrate concentration.

Question 19

A mutation in an allosteric enzyme causes the T (tense) state to be more stable than the R (relaxed) state. What is the most likely effect on the enzyme's activity curve?

Accepted Answer

The enzyme will require higher substrate concentrations to reach maximal activity, shifting the sigmoidal curve to the right.

Enzyme Kinetics and Allosteric Regulation: Study Notes

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