Question 1

Which of the following best describes the role of Mg$$^{2+}$$ ions in the active site of DNA polymerase I during DNA replication in prokaryotes?

Accepted Answer

Mg$$^{2+}$$ ions act as a cofactor that stabilizes the negative charges on the incoming dNTPs, facilitating nucleophilic attack during phosphodiester bond formation.

Question 2

Which class of enzyme catalyzes the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 3

A scientist discovers an enzyme that catalyzes the reaction S $$ightarrow P $$using H$$_2O or OH$^-$$ ions in the solution. Which class of enzyme does this belong to?

Accepted Answer

Hydrolase

Question 4

Which of the following statements about the Michaelis-Menten equation is correct?

Accepted Answer

At $$[S] = K_m$$, the reaction velocity $$v_0 is $$equal to $$\frac{1}{2}V_{max}.$$

Question 5

Given the Michaelis-Menten equation $$v_0$$ = \frac{V_{max}[S]}{K_m + [S]}$$, what is the initial velocity v_0$ if V$$_{max} = 10\ \mu$$M/min, K_m = 3$$\ \mu$$M, and $$[S] = 0.5$$ mM?

Accepted Answer

$$v_0$$ \approx 10\ \mu$$M/min

Question 6

Which of the following best describes the difference between the 'lock and key' and 'induced fit' models of enzyme-substrate interaction?

Accepted Answer

The 'lock and key' model suggests the enzyme active site is rigid and complementary to the substrate, while the 'induced fit' model proposes the active site is flexible and molds around the substrate upon binding.

Question 7

Which of the following is a correct statement about competitive inhibition?

Accepted Answer

A competitive inhibitor binds to the active site of the enzyme, increasing the apparent $$K_m$$ but not affecting $$V_{max}.$$

Question 8

Carbonic anhydrase operates optimally at pH 9. In the tissues of a sprinter at the end of their race, the pH is 7. What will happen to the enzyme's activity?

Accepted Answer

The enzyme's activity will decrease compared to its activity at pH 9.

Question 9

Which of the following is the correct Lineweaver-Burk equation for enzyme kinetics?

Accepted Answer

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

Question 10

An enzyme-catalyzed reaction is proceeding in the forward direction. If an enzyme catalyzing the reverse reaction is added in high concentration, what will happen to the amounts of products and reactants?

Accepted Answer

The reaction will approach equilibrium more quickly, with the final ratio of products to reactants determined by the equilibrium constant.

Question 11

Which of the following statements about $$K_{cat} is $$correct?

Accepted Answer

$$K_{cat} is $$the turnover number, representing the maximum number of substrate molecules converted to product per enzyme molecule per unit time.

Question 12

Which of the following best describes the effect of a noncompetitive inhibitor on enzyme kinetics?

Accepted Answer

A noncompetitive inhibitor decreases $$V_{max}$$ but does not change $$K_m.$$

Question 13

Which of the following is a correct description of the steady-state assumption in enzyme kinetics?

Accepted Answer

The concentration of the enzyme-substrate complex remains constant over the course of the reaction.

Question 14

A scientist compares two enzymes: beta-lactamase ($$k_{cat} = 800\ 	ext{s}^{-1}) $$and carbonic anhydrase ($$k_{cat} = 400,000\ 	ext{s}^{-1}). $$Which is the more efficient enzyme based on $$k_{cat}$$?

Accepted Answer

Carbonic anhydrase

Question 15

Which of the following best describes the effect of entropy on substrate binding to an enzyme?

Accepted Answer

Binding of a substrate to an enzyme decreases entropy, which is compensated by favorable enthalpic interactions.

Question 16

Which of the following is true regarding the preference of hexokinase versus glucokinase for glucose phosphorylation in glycolysis?

Accepted Answer

Hexokinase, with a lower $$K_m$$, is the preferable catalyst for glucose phosphorylation at low glucose concentrations.

Question 17

Which of the following is a characteristic of irreversible enzyme inhibition demonstrated by DIFP (diisopropyl fluorophosphate) on chymotrypsin?

Accepted Answer

DIFP covalently modifies the active site serine, permanently inactivating the enzyme.

Question 18

Which of the following best describes a ping-pong (double displacement) reaction mechanism?

Accepted Answer

One or more products are released before all substrates have bound to the enzyme.

Question 19

Which of the following is NOT a type of reversible enzyme inhibition?

Accepted Answer

Covalent modification of the active site

Enzyme Structure, Function, and Kinetics: Study Notes for Biochemistry

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