Question 1

Different enzymes that catalyze the same reaction are known as _____.

Accepted Answer

Isozymes are different enzymes that catalyze the same reaction but may differ in their kinetic properties or regulatory mechanisms.

Question 2

The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of _____.

Accepted Answer

Enzyme specificity refers to the ability of an enzyme to select and catalyze the reaction of a particular substrate among many possible molecules.

Question 3

How does a catalyst affect the overall $\Delta$G of an endergonic reaction?

Accepted Answer

A catalyst speeds up the rate of a reaction by lowering the activation energy but does not affect the overall change in free energy ($\Delta$G) of the reaction.

Question 4

How does a catalyst increase the rate of a reaction?

Accepted Answer

A catalyst increases the rate of a reaction by lowering the activation energy, allowing reacting molecules to more easily form the transition state.

Question 5

An organic molecule that is tightly bound to an enzyme and participates in an enzyme catalyzed reaction is specifically referred to as a _____.

Accepted Answer

A prosthetic group is an organic molecule that is tightly bound to an enzyme and is essential for its catalytic activity.

Question 6

Which of the following is seen in a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis?

Accepted Answer

In covalent catalysis, an intermediate is formed, leading to two distinct transition states. The energy of reactants and products is typically lower than that of the intermediate.

Question 7

In the enzyme catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a _____ residue in the active site of the enzyme.

Accepted Answer

A Schiff base is typically formed between a carbonyl group and an amine group, and lysine (Lys) contains an amine group in its side chain that can form a Schiff base with the ketone of acetoacetate.

Question 8

Of the following ions, which would be most likely to participate in metal ion catalysis?

Accepted Answer

Zn²⁺ is a transition metal ion and can participate in metal ion catalysis by forming coordination complexes with the substrate.

Question 9

In an enzyme mechanism that generates a negative charge in the transition state, which of the following would be most effective to have in the active site of the enzyme?

Accepted Answer

A transition metal cation can stabilize the negative charge in the transition state through electrostatic interactions.

Question 10

During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play?

Accepted Answer

During the formation of the acyl-enzyme intermediate, His acts first as a general base to deprotonate Ser, enhancing its nucleophilicity, and then as a general acid to donate a proton to the leaving group.

Question 11

Of all the species that enzymes bind, they are thought to bind most tightly to _____.

Accepted Answer

Enzymes are thought to bind most tightly to the transition states of the reactions they catalyze, as this helps to lower the activation energy and stabilize the transition state, facilitating the conversion of substrates to products.

Question 12

In the chymotrypsin mechanism, what is used to stabilize the negative charge on the carbonyl oxygen of the transition state?

Accepted Answer

The stabilization of the negative charge on the carbonyl oxygen in the transition state of the chymotrypsin mechanism is achieved through hydrogen bonding between the enzyme and the anion from the carbonyl oxygen, often referred to as the "oxyanion hole."

Question 13

If an enzyme rate increases 10-fold for every 5.7 kJ/mol decrease in the energy of activation, what rate increase would be observed if three H-bonds were stabilizing the transition state with each H-bond having a strength of 21 kJ/mol?

Accepted Answer

Each H-bond decreases the activation energy by 21 kJ/mol, so three H-bonds decrease it by 63 kJ/mol. Since the rate increases 10-fold for every 5.7 kJ/mol decrease, the rate increase is 10^(63/5.7) = 10^11.

Question 14

When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state?

Accepted Answer

A low-barrier hydrogen bond is a specific type of hydrogen bond that is stronger and shorter than a regular hydrogen bond, often observed in enzyme active sites to stabilize transition states.

Question 15

The enzyme hexokinase catalyzes a reaction where its substrates are completely sequestered from the aqueous environment allowing for interactions to occur between enzyme and substrates that would not normally occur in an aqueous environment. What term describes this type of catalysis?

Accepted Answer

The answer of The enzyme hexokinase catalyzes a reaction where...

Question 16

What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys?

Accepted Answer

Aspartate (Asp) in the specificity pocket of trypsin forms a salt bridge with the positively charged side chains of arginine (Arg) or lysine (Lys), allowing trypsin to specifically bind to these residues.

Question 17

Chymotrypsin has a large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind Ala or Gly. Which of the following amino acid substitutions changes the specificity pocket of chymotrypsin to that of elastase?

Accepted Answer

The answer of Chymotrypsin has a large specificity pocket to...

Question 18

Which protein in the blood is responsible for converting fibrinogen to fibrin?

Accepted Answer

Thrombin is the enzyme that converts fibrinogen into fibrin during the blood clotting process.

Question 19

Conversion of factor X to factor Xa represents a(n) _____ form of activation; binding of antithrombin to thrombin represents a(n) _____ form of inhibition.

Accepted Answer

Conversion of factor X to factor Xa is an irreversible activation as it involves proteolytic cleavage. Binding of antithrombin to thrombin is a reversible form of inhibition as it forms a complex that can dissociate.

Question 20

Which of the following is true regarding heparin?

Accepted Answer

Heparin is an allosteric activator of antithrombin, a sulfated polysaccharide, binds to both antithrombin and its target, and is used clinically as an anticoagulant.

Quiz 6: How Enzymes Work

Different enzymes that catalyze the same reaction are known as _____.

The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of _____.

How does a catalyst affect the overall $\Delta$ G of an endergonic reaction?

How does a catalyst increase the rate of a reaction?

An organic molecule that is tightly bound to an enzyme and participates in an enzyme catalyzed reaction is specifically referred to as a _____.

Which of the following is seen in a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis?

In the enzyme catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a _____ residue in the active site of the enzyme.

Of the following ions, which would be most likely to participate in metal ion catalysis?

In an enzyme mechanism that generates a negative charge in the transition state, which of the following would be most effective to have in the active site of the enzyme?

During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play?

Of all the species that enzymes bind, they are thought to bind most tightly to _____.

In the chymotrypsin mechanism, what is used to stabilize the negative charge on the carbonyl oxygen of the transition state?

If an enzyme rate increases 10-fold for every 5.7 kJ/mol decrease in the energy of activation, what rate increase would be observed if three H-bonds were stabilizing the transition state with each H-bond having a strength of 21 kJ/mol?

When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state?

The enzyme hexokinase catalyzes a reaction where its substrates are completely sequestered from the aqueous environment allowing for interactions to occur between enzyme and substrates that would not normally occur in an aqueous environment. What term describes this type of catalysis?

What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys?

Chymotrypsin has a large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind Ala or Gly. Which of the following amino acid substitutions changes the specificity pocket of chymotrypsin to that of elastase?

Which protein in the blood is responsible for converting fibrinogen to fibrin?

Conversion of factor X to factor Xa represents a(n) _ form of activation; binding of antithrombin to thrombin represents a(n) _ form of inhibition.

Which of the following is true regarding heparin?

Quiz 6: How Enzymes Work

Different enzymes that catalyze the same reaction are known as _____.

The ability for an enzyme to pick out one particular substrate from the myriad of molecules floating around its environment is an example of _____.

How does a catalyst affect the overall Δ\DeltaΔ G of an endergonic reaction?

How does a catalyst increase the rate of a reaction?

An organic molecule that is tightly bound to an enzyme and participates in an enzyme catalyzed reaction is specifically referred to as a _____.

Which of the following is seen in a reaction coordinate diagram for an enzyme-catalyzed reaction that uses covalent catalysis?

In the enzyme catalyzed decarboxylation of acetoacetate, a Schiff base is formed between the ketone of acetoacetate and a _____ residue in the active site of the enzyme.

Of the following ions, which would be most likely to participate in metal ion catalysis?

In an enzyme mechanism that generates a negative charge in the transition state, which of the following would be most effective to have in the active site of the enzyme?

During the first half of the chymotrypsin mechanism where the acyl-enzyme intermediate is formed, what role does His play?

Of all the species that enzymes bind, they are thought to bind most tightly to _____.

In the chymotrypsin mechanism, what is used to stabilize the negative charge on the carbonyl oxygen of the transition state?

If an enzyme rate increases 10-fold for every 5.7 kJ/mol decrease in the energy of activation, what rate increase would be observed if three H-bonds were stabilizing the transition state with each H-bond having a strength of 21 kJ/mol?

When the transition state is formed, what is the specific interaction observed between Asp and His that helps stabilize the transition state?

The enzyme hexokinase catalyzes a reaction where its substrates are completely sequestered from the aqueous environment allowing for interactions to occur between enzyme and substrates that would not normally occur in an aqueous environment. What term describes this type of catalysis?

What amino acid residue present in the specificity pocket allows trypsin to bind to peptides containing Arg or Lys?

Chymotrypsin has a large specificity pocket to bind the aromatic amino acids while elastase has a very small specificity pocket meant to bind Ala or Gly. Which of the following amino acid substitutions changes the specificity pocket of chymotrypsin to that of elastase?

Which protein in the blood is responsible for converting fibrinogen to fibrin?

Conversion of factor X to factor Xa represents a(n) _____ form of activation; binding of antithrombin to thrombin represents a(n) _____ form of inhibition.

Which of the following is true regarding heparin?

How does a catalyst affect the overall $\Delta$ G of an endergonic reaction?

Conversion of factor X to factor Xa represents a(n) _ form of activation; binding of antithrombin to thrombin represents a(n) _ form of inhibition.