Question 1

Which of the following best explains why enzymes increase the rate of biochemical reactions?

Accepted Answer

They decrease the free energy of the transition state ($$\Delta G$$^{\ddagger}$$), making it easier for the reaction to proceed.

Question 2

Which enzyme class is responsible for catalyzing the transfer of functional groups between molecules?

Accepted Answer

Transferases

Question 3

A patient with a deficiency in NAD$$^+$$ would most likely have impaired activity in which type of enzyme?

Accepted Answer

Oxidoreductases

Question 4

Which statement about enzyme specificity is CORRECT?

Accepted Answer

Enzyme specificity is dictated by the amino acid residues in the active site, leading to high stereo selectivity.

Question 5

Which of the following best describes the difference between a holoenzyme and an apoenzyme?

Accepted Answer

A holoenzyme is an enzyme with its cofactor and is active; an apoenzyme is the enzyme without the cofactor and is inactive.

Question 6

Which of the following is an example of acid-base catalysis in enzymatic reactions?

Accepted Answer

Histidine in RNase A acting as both a proton donor and acceptor during RNA cleavage.

Question 7

A mutation replaces Asp 52 with Asn in lysozyme. What is the most likely effect on enzyme activity?

Accepted Answer

The enzyme activity will decrease because Asp 52 is important for stabilizing the oxonium ion transition state.

Question 8

Which of the following best describes the role of metal ions in enzyme catalysis?

Accepted Answer

They can stabilize negative charges, orient substrates, and mediate oxidation-reduction reactions.

Question 9

Which of the following is a correct statement about the lock and key hypothesis?

Accepted Answer

It suggests that the enzyme and substrate have complementary, preformed shapes that fit exactly.

Question 10

Which of the following is NOT a property that distinguishes enzymes from non-biological chemical catalysts?

Accepted Answer

Enzymes require extreme temperatures and pressures to function.

Question 11

Which of the following best describes the effect of Mg$$^{2+} in $$DNA polymerase catalysis?

Accepted Answer

Mg$$^{2+}$$ shields the negative charge on phosphate groups, facilitating nucleophilic attack during DNA synthesis.

Question 12

Which of the following is an example of covalent catalysis?

Accepted Answer

The formation of a Schiff base (imine) intermediate between an enzyme lysine and a substrate carbonyl group.

Question 13

Which of the following statements about enzyme catalysis through proximity and orientation effects is CORRECT?

Accepted Answer

Proper orientation of reactants in the active site is the dominant factor in increasing the reaction rate.

Question 14

A solution contains histidine with a pKa of 6.0. At pH 7.0, what is the ratio of protonated to unprotonated histidine? (Use the Henderson-Hasselbalch equation: $$pH = pK_a + \log \left( \frac{[A^-]}{[HA]} \right))$$

Accepted Answer

$$1:10 ($$unprotonated:protonated)

Question 15

Which of the following is a real-life example of an enzyme using metal ion catalysis?

Accepted Answer

Carbonic anhydrase using Zn$$^{2+} to $$convert CO$$_2 to $$bicarbonate in blood.

Question 16

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

Accepted Answer

Enzymes lower the activation energy ($$\Delta G$$^{\ddagger}$$) but do not change the overall free energy change ($$\Delta G$$) of the reaction.

Question 17

Which of the following best describes the induced fit model of enzyme-substrate interaction?

Accepted Answer

The substrate induces a conformational change in the enzyme, resulting in tighter binding.

Question 18

Which of the following is a function of cofactors in enzymatic reactions?

Accepted Answer

They provide reactive components such as proton sources, functional groups, or charge stabilization necessary for catalysis.

Question 19

Which of the following is a correct example of enzyme nomenclature based on substrate?

Accepted Answer

Lactase

Enzymology: Structure, Function, and Catalysis

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