$$\text{Lactose} + \text{H}_2\text{O} \rightarrow \text{Galactose} + \text{Glucose}$$

Hydrolysis of phosphoester bonds: $$\text{R-O-PO}_3$$^{2-}$$ + \text{H}_2\text{O} \rightarrow \text{R-OH} + \text{HOPO}_3$$^{2-}$$

Question 1

Which of the following best describes the role of Zn$$^{2+} in $$the catalytic mechanism of metalloproteases?

Accepted Answer

Zn$$^{2+}$$ coordinates and activates water for nucleophilic attack, and stabilizes the oxyanion intermediate.

Question 2

A patient is diagnosed with lactose intolerance due to a deficiency in $$eta-$$galactosidase. Which reaction is impaired in this patient?

Accepted Answer

$$	ext{Lactose} + 	ext{H}_2	ext{O} ightarrow 	ext{Galactose} + 	ext{Glucose}$$

Question 3

Which of the following enzymes utilizes a catalytic triad consisting of Ser, His, and Asp in its active site?

Accepted Answer

Serine proteases

Question 4

In the mechanism of acid proteases, what is the primary function of the Asp residue?

Accepted Answer

Asp activates a water molecule for direct attack on the carbonyl carbon of the peptide bond.

Question 5

Which of the following best explains why cysteine proteases use a catalytic dyad rather than a triad?

Accepted Answer

The thiol group of cysteine is sufficiently nucleophilic and does not require additional activation by a third residue.

Question 6

Which of the following statements about glycosidases is correct?

Accepted Answer

Glycosidases catalyze the hydrolysis of glycosidic linkages in carbohydrates.

Question 7

During the hydrolysis of a peptide bond by a serine protease, which residue acts as the nucleophile?

Accepted Answer

Serine

Question 8

Which enzyme mechanism involves two sequential $$S_N2$$ reactions leading to retention of configuration at the anomeric carbon?

Accepted Answer

Lysozyme

Question 9

A mutation in the active site of hexokinase prevents the conformational change upon glucose binding. What is the most likely consequence?

Accepted Answer

The enzyme will remain in an inactive conformation, reducing phosphorylation of glucose.

Question 10

Which of the following is a correct description of the reaction catalyzed by phosphatases?

Accepted Answer

Hydrolysis of phosphoester bonds: $$	ext{R-O-PO}_3$$^{2-}$$ + 	ext{H}_2	ext{O} ightarrow 	ext{R-OH} + 	ext{HOPO}_3$$^{2-}$$

Question 11

Which of the following enzymes is responsible for cleaving the peptide bond between Arg and Gly in fibrinogen during blood coagulation?

Accepted Answer

Thrombin

Question 12

Which of the following best describes the induced fit mechanism of hexokinase?

Accepted Answer

Binding of glucose causes a conformational change that brings the enzyme into its active conformation.

Question 13

Which of the following is NOT a function of hydrolases?

Accepted Answer

Catalyzing the transfer of phosphoryl groups from ATP to a substrate

Question 14

Which of the following statements about nucleases is correct?

Accepted Answer

Nucleases catalyze the hydrolysis of phosphodiester bonds in nucleic acids.

Question 15

Which of the following enzymes is most likely to be active in the small intestine and cleave peptide bonds after small hydrophobic amino acids?

Accepted Answer

Chymotrypsin

Question 16

Which of the following is a correct description of the reaction catalyzed by acetylcholinesterase?

Accepted Answer

$$	ext{Acetylcholine} + 	ext{H}_2	ext{O} ightarrow 	ext{Choline} + 	ext{Acetate}$$

Question 17

Which of the following best describes the mechanism of action of lysozyme?

Accepted Answer

Lysozyme hydrolyzes glycosidic bonds between N-acetylmuramic acid and N-acetylglucosamine in bacterial cell walls.

Question 18

Which of the following is a distinguishing feature of acid proteases compared to other protease classes?

Accepted Answer

They use Asp residues to activate water for nucleophilic attack.

Question 19

Which of the following reactions is catalyzed by a phosphotransferase such as hexokinase?

Accepted Answer

$$	ext{ATP} + 	ext{Glucose} ightarrow 	ext{ADP} + 	ext{Glucose-6-phosphate}$$

Enzymatic Reaction Mechanisms Part II: Proteases, Hydrolases, and Their Mechanisms

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