Question 1

Which of the following best describes the role of a co-factor in enzyme catalysis?

Accepted Answer

A co-factor is a non-protein molecule that binds to the enzyme's active site and directly participates in the chemical reaction.

Question 2

Given the Michaelis-Menten equation $$v = \frac{V_{max}[S]}{K_m + [S]}$$, what happens to $$V_{max}$$ and $$K_m in $$the presence of a competitive inhibitor?

Accepted Answer

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

Question 3

An enzyme catalyzes the reaction $$E + S \rightleftharpoons ES \rightarrow E + P. If $$the rate constants are $$k_1$$, $$k_{-1}$$, and $$k_2$$, which of the following expressions correctly defines the Michaelis constant $$K_m$$?

Accepted Answer

$$K_m = \frac{k_{-1} + k_2$}{k_1$}$$

Question 4

If $$V_{max}$$ for a reaction is $$13.0\ \mu M\ s$$^{-1}$$ and the total enzyme concentration is 2$$\ mM$$, what is the turnover number (k$$_{cat}$$)?

Accepted Answer

$$k_{cat} = \frac{V_{max}}{[E]_{total}} = \frac{13.0\ \mu M\ s$$^{-1}$$}{2\ mM} = 6.5\ s$$^{-1}$$

Question 5

Sulphapyridine acts as an antibiotic by inhibiting an enzyme that uses p-amino benzoic acid as a substrate. What type of inhibitor is sulphapyridine?

Accepted Answer

Competitive inhibitor

Question 6

Which of the following best explains why sulphapyridine is a competitive inhibitor for the enzyme that uses p-amino benzoic acid?

Accepted Answer

Sulphapyridine structurally resembles p-amino benzoic acid and competes for binding at the active site.

Question 7

In a double-reciprocal (Lineweaver-Burk) plot, how does the presence of a competitive inhibitor affect the plot compared to the uninhibited reaction?

Accepted Answer

The $$y-$$intercept ($$1/V_{max}) $$remains the same, but the slope increases due to increased $$K_m.$$

Question 8

Which of the following amino acid residues is most likely to interact with a substrate/inhibitor containing a carboxyl group?

Accepted Answer

Arginine

Question 9

If a hexagonal substrate is heavily substituted with hydrophilic functional groups (like $$-COOH$$), how will this affect its interaction with an enzyme active site lined with hydrophobic residues?

Accepted Answer

The substrate will bind less efficiently due to unfavorable hydrophilic-hydrophobic interactions.

Question 10

Which of the following statements about activation energy is correct?

Accepted Answer

Activation energy is the difference between the energy levels of the ground state and the transition state.

Question 11

For an enzyme-catalyzed reaction, which of the following is the rate-limiting step?

Accepted Answer

The step with the highest activation energy barrier.

Question 12

Which of the following is true regarding the specificity of enzyme active sites?

Accepted Answer

Active sites are formed by specific amino acid residues that interact with the substrate via non-covalent forces.

Question 13

If the enzyme concentration is doubled in a reaction following Michaelis-Menten kinetics, what happens to $$V_{max}$$ and $$K_m$$?

Accepted Answer

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

Question 14

Which of the following best describes the effect of a non-competitive inhibitor on enzyme kinetics?

Accepted Answer

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

Question 15

Which of the following equations correctly represents enzyme efficiency?

Accepted Answer

$$	ext{Enzyme efficiency} = \frac{k_{cat}}{K_m}$$

Question 16

Which of the following is most likely to be recognized by the enzyme DD-transpeptidase when comparing the structures of D-Ala-D-Ala and penicillin?

Accepted Answer

The peptide bond between the two D-Ala residues.

Question 17

Which of the following is a plausible reason why penicillin inhibits DD-transpeptidase?

Accepted Answer

Penicillin mimics the structure of D-Ala-D-Ala, allowing it to bind to the active site and block substrate access.

Question 18

Which of the following best describes the trend in initial velocity ($$v) $$versus substrate concentration $$[S]$$ for an enzyme following Michaelis-Menten kinetics?

Accepted Answer

Initial velocity increases rapidly at low $$[S]$$ and approaches $$V_{max}$$ asymptotically at high $$[S].$$

Question 19

Which of the following is a correct interpretation of the turnover number ($$k_{cat}) $$for an enzyme?

Accepted Answer

$$k_{cat} is $$the number of substrate molecules converted to product per enzyme molecule per second.

Enzyme Kinetics, Inhibition, and Substrate Recognition: Study Notes

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