Question 1

Which of the following best describes general acid-base catalysis in enzyme mechanisms?

Accepted Answer

A catalytic group on the enzyme can act as both a proton donor and acceptor, depending on the reaction step.

Question 2

Which of the following amino acid side chains is LEAST likely to participate in general acid-base catalysis at physiological pH?

Accepted Answer

Phenylalanine

Question 3

A serine protease catalyzes peptide bond hydrolysis by forming a transient covalent bond with the substrate. Which type of catalysis does this illustrate?

Accepted Answer

Covalent catalysis

Question 4

Which of the following is a correct example of a metalloenzyme and its tightly bound metal ion?

Accepted Answer

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

Question 5

Which of the following best explains why resonance stabilization is important for carbanion intermediates in enzyme-catalyzed reactions?

Accepted Answer

It delocalizes the negative charge, lowering the energy of the intermediate.

Question 6

Which of the following is a typical electrophilic center attacked by a nucleophile in biochemical reactions?

Accepted Answer

The carbonyl carbon of an aldehyde

Question 7

A reaction mechanism involves the abstraction of a proton by a base, followed by nucleophilic attack on a carbonyl carbon. Which two types of catalysis are most likely involved?

Accepted Answer

Acid-base catalysis and covalent catalysis

Question 8

Which of the following statements about enzyme classification (EC numbers) is TRUE?

Accepted Answer

EC numbers provide a systematic way to name enzymes based on the type of reaction they catalyze.

Question 9

In a Claisen ester condensation, which intermediate is stabilized to facilitate carbon-carbon bond formation?

Accepted Answer

Carbanion

Question 10

Which of the following best describes the role of metal ions in metalloenzymes?

Accepted Answer

They stabilize negative charges in the transition state and can participate in redox chemistry.

Question 11

Which of the following is an example of a group transfer reaction in biochemistry?

Accepted Answer

Transfer of a phosphate group from ATP to glucose by hexokinase

Question 12

During the aldol condensation in glycolysis, which type of intermediate is formed and stabilized?

Accepted Answer

Carbanion (enolate)

Question 13

Which of the following best describes a nucleophilic attack in a biochemical reaction?

Accepted Answer

A negatively charged or electron-rich atom donates an electron pair to an electrophilic center.

Question 14

Which of the following is a key feature of elimination reactions in biochemistry?

Accepted Answer

Removal of a group from a substrate, often resulting in the formation of a double bond

Question 15

A mutation in an enzyme's active site replaces a histidine with phenylalanine. Which catalytic mechanism is most likely to be disrupted?

Accepted Answer

Acid-base catalysis

Question 16

Which of the following best explains why the environment of an enzyme's active site can alter the pK$$_a$$ values of amino acid side chains?

Accepted Answer

Interactions with other residues and the substrate can stabilize or destabilize charged forms, shifting pK$$_a$$ values.

Question 17

Which of the following is a correct description of a Schiff base in enzyme catalysis?

Accepted Answer

A covalent intermediate formed between a carbonyl group and a primary amine, often from lysine.

Question 18

Which of the following is an example of an isomerization reaction catalyzed by an enzyme?

Accepted Answer

Conversion of glucose-6-phosphate to fructose-6-phosphate

Question 19

Which of the following best describes the difference between metalloenzymes and metal-activated enzymes?

Accepted Answer

Metalloenzymes have tightly bound metal ions, while metal-activated enzymes have loosely bound metal ions.

Question 20

Which of the following is a plausible mechanism by which an enzyme could stabilize a negative charge on an enolate intermediate?

Accepted Answer

By positioning a positively charged metal ion or hydrogen bond donor near the oxygen atom

Enzyme Catalysis Mechanisms and Reaction Types in Biochemistry

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