Question 1

A patient is diagnosed with a genetic disorder that impairs the function of enzymes responsible for transferring phosphate groups from ATP to other molecules. Which class of enzyme is most likely affected in this patient?

Accepted Answer

Class 2: Transferases

Question 2

Which of the following general reaction formulas best represents the action of a hydrolase enzyme?

Accepted Answer

$$A-B + H_2O \rightarrow A-H + B-OH$$

Question 3

A researcher is studying an enzyme that catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate, which are isomers. To which enzyme class does this enzyme belong?

Accepted Answer

Class 5: Isomerases

Question 4

Which of the following statements correctly distinguishes between lyases (synthases) and ligases (synthetases)?

Accepted Answer

Lyases catalyze bond formation or cleavage without ATP, while ligases require ATP hydrolysis to join molecules.

Question 5

Which subclass of enzymes would most likely catalyze the following reaction: $$R-COOH + R'-NH_2$ \rightarrow R-CONH-R' + H_2O$$?

Accepted Answer

Class 6: Ligases (specifically C-N Ligases)

Question 6

A biochemist observes an enzyme that catalyzes the following reaction: $$A-B + C \rightarrow A + B-C. $$Which class does this enzyme belong to?

Accepted Answer

Class 2: Transferases

Question 7

Which enzyme class is primarily responsible for catalyzing the addition or removal of groups to form double bonds, without the use of water or electron transfer?

Accepted Answer

Class 4: Lyases

Question 8

A laboratory test reveals an enzyme that catalyzes the following reaction: $$A (reduced) + B (oxidized) \rightarrow A (oxidized) + B (reduced). $$Which subclass might this enzyme belong to?

Accepted Answer

Dehydrogenases (a subclass of Oxidoreductases)

Question 9

Which of the following best describes the chemical mechanism of isomerases?

Accepted Answer

They rearrange the spatial positioning or connectivity of atoms within a molecule without changing its molecular formula.

Question 10

A pharmaceutical company is developing a drug that inhibits the enzyme responsible for the hydrolysis of peptide bonds in proteins. Which enzyme subclass is the drug targeting?

Accepted Answer

Peptidases (a subclass of Hydrolases)

Question 11

Which of the following reactions would most likely be catalyzed by a ligase enzyme?

Accepted Answer

$$A + B + ATP \rightarrow A-B + ADP + P$$

Question 12

A mutation in a gene leads to the loss of function of a monooxygenase enzyme. Which class of enzyme activity would be directly affected?

Accepted Answer

Class 1: Oxidoreductases

Question 13

Which of the following is a key difference between the general reaction formulas of hydrolases and lyases?

Accepted Answer

Hydrolases use water to break bonds ($$A-B + H_2O \rightarrow A-H + B-OH$$), while lyases do not use water ($$A + B \rightarrow A-B or $$vice versa).

Question 14

A scientist is studying an enzyme that catalyzes the following reaction: $$A ightarrow 	ext{Iso-A}. $$Which enzyme class does this reaction represent?

Accepted Answer

Class 5: Isomerases

Question 15

Which of the following best describes the role of kinases in cellular metabolism?

Accepted Answer

They transfer phosphate groups from ATP to other molecules.

Question 16

A metabolic pathway involves the non-hydrolytic cleavage of a carbon-carbon bond, resulting in the formation of a double bond. Which enzyme class is most likely responsible for this reaction?

Accepted Answer

Class 4: Lyases

Question 17

Which of the following enzyme classes is directly involved in catalyzing the formation of glycosidic bonds during the synthesis of polysaccharides?

Accepted Answer

Class 2: Transferases (specifically Glycosyltransferases)

Question 18

A clinical case involves a deficiency in an enzyme that catalyzes the following reaction: $$A + B + GTP \rightarrow A-B + GDP + P. $$Which of the following statements is most accurate regarding this enzyme?

Accepted Answer

It is a ligase (synthetase) that requires nucleoside triphosphate hydrolysis for bond formation.

Question 19

Which of the following is NOT a typical function of oxidoreductases?

Accepted Answer

Transferring methyl groups between molecules

Question 20

A new enzyme is discovered that catalyzes the following reaction: $$A-B + H_2O \rightarrow A-H + B-OH. $$The enzyme is found to be highly specific for ester bonds. Which subclass does it most likely belong to?

Accepted Answer

Esterases (a subclass of Hydrolases)

The Six Major Classes of Enzymes: Structure, Function, and Classification

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