Question 1

Which of the following statements best explains why the conversion of sucrose to CO$$_2$$ and water, despite having a large negative $$\Delta G'^{\circ}$$, does not occur spontaneously in cells?

Accepted Answer

There is a very large activation energy barrier.

Question 2

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

Accepted Answer

Enzymes alter the equilibrium constant of a reaction.

Question 3

What does an enzyme change relative to an uncatalyzed reaction?

Accepted Answer

The rate of the reaction

Question 4

Which of the following best describes the effect of an enzyme on the activation energy ($$\Delta G$$^{\circ\ddagger}$$) and the standard free energy change ($$\Delta $$G^{\circ}) of a $$reaction?

Accepted Answer

$$\Delta G$$^{\circ\ddagger}$$ is lowered, but $$\Delta $$G^{\circ}$$ remains unchanged.

Question 5

Which class of enzyme catalyzes the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 6

A reaction catalyzed by an enzyme has a small, negative $$\Delta G$$^{\circ}$$ but proceeds very slowly. What can be concluded?

Accepted Answer

The reaction is spontaneous but slow.

Question 7

Which of the following is a common feature of the active site of an enzyme?

Accepted Answer

It is complementary in shape and charge to the substrate.

Question 8

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

Accepted Answer

They can orient substrates, mediate redox reactions, and stabilize negative charges.

Question 9

Which of the following amino acids is LEAST likely to affect enzyme function if it replaces a Glu residue in the active site?

Accepted Answer

Gly

Question 10

Which of the following statements about enzyme stereospecificity is correct?

Accepted Answer

Enzymes are highly specific for the stereochemistry of their substrates due to their own chirality.

Question 11

Which of the following is an example of a coenzyme acting as a transient carrier of atoms or functional groups?

Accepted Answer

NAD$$^+ in $$oxidation-reduction reactions

Question 12

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

Accepted Answer

Covalent catalysis

Question 13

Why are transition state analogs often potent enzyme inhibitors?

Accepted Answer

They resemble the transition state and bind with higher affinity than the substrate.

Question 14

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

Accepted Answer

Enzymes stabilize the transition state, lowering the activation energy.

Question 15

Which of the following is NOT a way in which enzymes accelerate chemical reactions?

Accepted Answer

By increasing the temperature of the reaction.

Question 16

Which of the following best explains why enzymes rarely produce side products?

Accepted Answer

Enzymes are highly specific for their substrates and reactions.

Question 17

Which of the following is a real-life example of an enzyme requiring a metal ion cofactor for activity?

Accepted Answer

Carbonic anhydrase requiring Zn$$^{2+}$$

Question 18

Which of the following statements about enzyme regulation is correct?

Accepted Answer

Allosteric effectors can increase or decrease enzyme activity.

Question 19

Which of the following best describes the role of proximity and orientation effects in enzyme catalysis?

Accepted Answer

They increase the effective concentration of reactants and orient them for optimal reaction.

Question 20

Which of the following is an example of an enzyme using acid-base catalysis?

Accepted Answer

RNase A hydrolyzing RNA

Enzymes and Catalytic Mechanisms: Biochemistry Study Notes

Guida di studio - Domande di pratica

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