Question 1

Which class of enzyme is primarily responsible for catalyzing the transfer of electrons from one molecule to another, as shown in the oxidation-reduction reaction below?

$\mathrm{A_{red} + B_{ox} \rightarrow A_{ox} + B_{red}}$

Accepted Answer

Oxidoreductases

Question 2

A scientist is studying an enzyme that catalyzes the hydrolysis of a peptide bond in a protein. To which enzyme class does this enzyme most likely belong?

Accepted Answer

Hydrolases

Question 3

Which of the following best describes the reaction catalyzed by ligases?

$\mathrm{A + B + XTP \rightarrow A{-}B + XDP}$

Accepted Answer

Joining two molecules by the formation of new bonds, usually with the hydrolysis of ATP or a similar compound

Question 4

Which enzyme class would catalyze the following reaction?

$\mathrm{Glucose{-}6{-}phosphate \rightarrow Fructose{-}6{-}phosphate}$

Accepted Answer

Isomerases

Question 5

A reaction involves the transfer of a phosphate group from ATP to glucose, forming glucose-6-phosphate. Which enzyme class is responsible for this reaction?

Accepted Answer

Transferases

Question 6

Which of the following is NOT a function of hydrolases?

Accepted Answer

Transfer of electrons between molecules

Question 7

Which enzyme class is most likely to catalyze the following reaction?

$\mathrm{A{-}B \rightarrow A + B}$ (without the addition of water or oxidation/reduction)

Accepted Answer

Lyases

Question 8

A mutation in a gene leads to the inability to convert L-alanine to D-alanine. Which enzyme class is most likely affected?

Accepted Answer

Isomerases

Question 9

Which of the following reactions is an example of an oxidoreductase-catalyzed process?

$\mathrm{NADH + H^+ + 1/2 O_2 \rightarrow NAD^+ + H_2O}$

Accepted Answer

Oxidoreductase

Question 10

Which enzyme class would be responsible for catalyzing the following reaction?

$\mathrm{C{-}C{-}C{-}C{-}C{-}C \rightarrow C{-}C{-}C + C{-}C{-}C}$ (without water or oxidation/reduction)

Accepted Answer

Lyases

Question 11

Which of the following best describes the main function of transferases?

Accepted Answer

Transfer of a specific group (such as a phosphate or methyl group) from one substrate to another

Question 12

Which enzyme class is responsible for catalyzing the following reaction?

$\mathrm{A{-}B + H_2O \rightarrow A{-}OH + B{-}H}$

Accepted Answer

Hydrolases

Question 13

A reaction involves the conversion of citrate to isocitrate. Which enzyme class is most likely involved?

Accepted Answer

Isomerases

Question 14

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

Accepted Answer

Lyases catalyze the nonhydrolytic removal or addition of groups to substrates, while hydrolases catalyze bond cleavage using water

Question 15

Which enzyme class would catalyze the following reaction?

$\mathrm{A{-}B + C \rightarrow A + B{-}C}$

Accepted Answer

Transferases

Question 16

Which of the following reactions is most likely catalyzed by a ligase?

$\mathrm{CO_2 + ATP + Acetyl{-}CoA \rightarrow Malonyl{-}CoA + ADP + P_i}$

Accepted Answer

Ligase

Question 17

Which enzyme class is responsible for catalyzing the following reaction?

$\mathrm{A{-}B \rightarrow A{-}B'}$ (where $B$ and $B'$ are isomers)

Accepted Answer

Isomerases

Question 18

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

Accepted Answer

They catalyze the transfer of electrons, often using cofactors such as NAD+ or FAD

Question 19

A reaction involves the conversion of fumarate to malate by the addition of water. Which enzyme class is most likely responsible?

Accepted Answer

Lyases

Question 20

Which enzyme class would catalyze the following reaction?

$\mathrm{A + B \rightarrow A{-}B}$ (with the input of energy from ATP)

Accepted Answer

Ligases

Six Classes of Enzymes: Structure, Function, and Examples

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