Q: An enzyme-catalyzed reaction has a $$K_m of 2 mM $$and a $$V_{max} of 100$$ μmol/min. What is the initial velocity ($$v_0) $$when the substrate concentration $$[S] is 2 mM$$? Use the Michaelis-Menten equation: $$ v_0$ = \frac{V_{max} [S]}{K_m + [S]} $$

$$ v_0$ = \frac{100 \times 2}{2 + 2} = 50 \ \mu mol/min $$

Question 1

Which of the following best describes the induced-fit model of enzyme activity?

Accepted Answer

The enzyme changes its shape slightly to better fit the substrate upon binding.

Question 2

A patient with gout is treated with allopurinol. Which enzyme does allopurinol inhibit, and what is the effect on uric acid production?

Accepted Answer

Allopurinol inhibits xanthine oxidase, decreasing uric acid production.

Question 3

Which of the following statements about ribozymes is correct?

Accepted Answer

Ribozymes are RNA molecules with catalytic activity.

Question 4

An enzyme-catalyzed reaction has a $$K_m of 2 mM $$and a $$V_{max} of 100$$ μmol/min. What is the initial velocity ($$v_0) $$when the substrate concentration $$[S] is 2 mM$$? Use the Michaelis-Menten equation:

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

Accepted Answer

$$ v_0$ = \frac{100 	imes 2}{2 + 2} = 50 \ \mu mol/min $$

Question 5

Which of the following best explains why enzymes do not alter the overall free energy change ($$\Delta G) of a $$reaction?

Accepted Answer

Enzymes lower the activation energy but do not affect the energy difference between reactants and products.

Question 6

A researcher adds a competitive inhibitor to an enzyme reaction. Which of the following changes would you expect in the Michaelis-Menten plot?

Accepted Answer

$$V_{max}$$ remains unchanged, $$K_m$$ increases.

Question 7

Which of the following is an example of enzyme regulation by covalent modification?

Accepted Answer

Phosphorylation of glycogen phosphorylase by a protein kinase.

Question 8

A patient has a mutation that prevents the proteolytic cleavage of pancreatic enzymes. What is the most likely physiological consequence?

Accepted Answer

Impaired digestion due to inactive pancreatic enzymes.

Question 9

Which of the following best describes the role of cofactors in enzyme activity?

Accepted Answer

Cofactors are non-protein molecules that assist enzymes in catalysis.

Question 10

A cell is exposed to a noncompetitive inhibitor. Which of the following changes would you expect in the enzyme kinetics?

Accepted Answer

$$V_{max}$$ decreases, $$K_m$$ remains unchanged.

Question 11

Which of the following scenarios best illustrates feedback inhibition in a metabolic pathway?

Accepted Answer

The end product of a pathway binds to and inhibits the first enzyme in the pathway.

Question 12

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

The active site of the enzyme has a unique shape and chemical environment that only fits specific substrates.

Question 13

A scientist measures the turnover number ($$k_{cat}) of an $$enzyme as $$500 \ s$$^{-1}$$. What does this value represent?

Accepted Answer

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

Question 14

Which of the following changes would most likely increase the rate of an enzyme-catalyzed reaction that is currently below its optimal temperature?

Accepted Answer

Increasing the temperature toward the enzyme's optimum.

Question 15

Which of the following best describes the metastable state in the context of enzyme-catalyzed reactions?

Accepted Answer

A state where the substrate has enough energy to react but does not spontaneously convert to product due to a high activation energy barrier.

Question 16

A mutation causes an enzyme's active site to become less complementary to its substrate. Which of the following is the most likely effect on the enzyme's $$K_m$$ and $$V_{max}$$?

Accepted Answer

$$K_m$$ increases, $$V_{max}$$ remains unchanged.

Question 17

Which of the following is a real-life example of allosteric regulation?

Accepted Answer

ATP binding to phosphofructokinase to decrease its activity in glycolysis.

Question 18

Which of the following best describes the effect of pH on enzyme activity?

Accepted Answer

Each enzyme has an optimal pH at which its activity is maximal.

Question 19

Which of the following statements about irreversible inhibitors is correct?

Accepted Answer

Irreversible inhibitors bind covalently to the enzyme, permanently inactivating it.

Question 20

A patient is found to have a deficiency in a coenzyme required for hexokinase activity. Which of the following is the most likely consequence?

Accepted Answer

Decreased phosphorylation of glucose in glycolysis.

Enzymes: Structure, Function, and Regulation (Chapter 6 Study Notes)

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