Question 1

Which experimental discovery provided definitive evidence that enzymes are proteins?

Accepted Answer

The isolation and crystallization of urease by James Sumner

Question 2

Alcohol dehydrogenase catalyzes the reversible redox reaction interconverting acetaldehyde and ethanol. Which cofactor is required for this reaction?

Accepted Answer

NAD+ (nicotinamide adenine dinucleotide)

Question 3

Which property of enzymes allows them to accelerate reaction rates by up to $$10^{17}-$$fold compared to uncatalyzed reactions?

Accepted Answer

Their ability to lower the activation energy $$\Delta G$$^{\ddagger}$$

Question 4

Which of the following statements best describes the role of binding energy in enzyme catalysis?

Accepted Answer

Binding energy stabilizes the transition state, thereby lowering $$\Delta G$$^{\ddagger}$$

Question 5

Which of the following is NOT a typical catalytic strategy employed by enzymes?

Accepted Answer

Increasing the reaction equilibrium constant $$K'$$

Question 6

A mutation in the active site of alcohol dehydrogenase replaces a zinc-coordinating cysteine with alanine. What is the most likely effect on enzyme activity?

Accepted Answer

The enzyme will lose its ability to bind the zinc ion, resulting in decreased or abolished activity

Question 7

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

Accepted Answer

The active site of the enzyme is complementary to the transition state of the substrate

Question 8

Which of the following is an example of a ribozyme?

Accepted Answer

RNA molecules that catalyze chemical reactions

Question 9

Which equation best describes the rate of a first-order enzyme-catalyzed reaction?

Accepted Answer

$$v = k[S]$$

Question 10

Which of the following is a real-world example of enzyme inhibition used in medicine?

Accepted Answer

Statins inhibiting HMG-CoA reductase to lower cholesterol

Question 11

Which of the following statements about cofactors is TRUE?

Accepted Answer

Cofactors can be metal ions or small organic molecules required for enzyme activity

Question 12

Which catalytic strategy involves the transient formation of a covalent bond between the enzyme and substrate?

Accepted Answer

Covalent catalysis

Question 13

Which of the following best describes the effect of enzymes on the thermodynamics of a reaction?

Accepted Answer

Enzymes lower the activation energy $$\Delta G$$^{\ddagger}$$ but do not change $$\Delta G$$

Question 14

Which of the following is a consequence of enzyme regulation in cells?

Accepted Answer

Enzyme activity can be modulated by inhibitors, activators, or covalent modification

Question 15

Which of the following is a function of metal ion cofactors in enzyme catalysis?

Accepted Answer

They stabilize negative charges and can act as Lewis acids

Question 16

Which of the following best explains the concept of 'orbital steering' in enzyme catalysis?

Accepted Answer

Enzymes align the orbitals involved in bond formation to accelerate the reaction

Question 17

Which of the following is an example of a reaction catalyzed by transferases?

Accepted Answer

Transfer of a phosphate group from ATP to a protein

Question 18

Which of the following statements about enzyme-catalyzed reactions is FALSE?

Accepted Answer

Enzymes change the equilibrium position of the reaction

Question 19

Which of the following is a real-world example of enzyme inhibition in agriculture?

Accepted Answer

Glyphosate inhibiting EPSP synthase in plants

Question 20

Which of the following best describes the role of transition state stabilization in enzyme catalysis?

Accepted Answer

Enzymes bind the transition state with higher affinity than the substrate, lowering $$\Delta G$$^{\ddagger}$$

Catalysis by Enzymes: Structure, Function, and Mechanisms

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