Question 1

In which way is the transition state of an enzyme-catalyzed reaction different from the transition state of the corresponding uncatalyzed reaction?

Accepted Answer

A)  It has a higher free energy content.
B)  It has less chemical stability and is therefore more reactive.
C)  It is more similar to the conformation of the substrate, as a result of induced fit.
D)  It is energetically more stable, because it makes favorable interactions with the enzyme.
E)  It participates in the reaction by exchanging a proton with the substrate, in a process that is known as general acid-base catalysis.F) A) and D)
G) A) and C)

Question 2

Neviripine is a drug for human immunodeficiency virus (HIV)  infection that is a noncompetitive inhibitor of reverse transcriptase.As a noncompetitive inhibitor, it:

Accepted Answer

A)  Binds to the same site on the enzyme as the substrate.
B)  Reduces the Km of the substrate.
C)  Forms a covalent bond with the enzyme.
D)  Does not bond to the enzyme in the absence of substrate.
E)  Moves the intercept on the 1/v axis of the Lineweaver-Burk plot farther away from the X-Y intersection.F) A) and C)
G) A) and E)

Question 3

C.G.is a 30-year-old retired stockbroker who has developed possible skin cancer while sailing in Polynesia.A skin biopsy is analyzed for cyclin-dependent kinase activity at different concentrations of the cosubstrate adenosine triphosphate (ATP) .The results are shown in Figure 4.7.  The apparent effect of the drug on C.G.'s kinase activity is to:

Accepted Answer

A)  Reduce the Vmax of the enzyme.
B)  Increase the Vmax of the enzyme.
C)  Reduce the Km of the enzyme.
D)  Increase the Km of the enzyme.
E)  Allosterically activate the kinase.F) A) and E)
G) None of the above

Question 4

The maximal reaction rate (Vmₐₓ)  is a kinetic property of an enzymatic reaction that depends on the incubation conditions, the enzyme concentration, and:

Accepted Answer

A)  The standard free energy change (DG0')  of the reaction.
B)  The entropy change that accompanies the reaction.
C)  The ratio between the kinetic rate constants for the forward and backward reactions.
D)  Km.
E)  The turnover number of the enzyme.F) None of the above
G) A) and D)

Question 5

Most NAD-using enzymes are named as:

Accepted Answer

A)  Transferases.
B)  Dehydrogenases.
C)  Carboxylases.
D)  Oxygenases.
E)  Lyases.F) D) and E)
G) None of the above

Question 6

The rate of a typical enzyme-catalyzed reaction:

Accepted Answer

A)  Is independent of pH over a broad range of pH values.
B)  Is approximately proportional to the substrate concentration as long as the substrate concentration is much lower than the Michaelis constant (Km) .
C)  Rises by a factor of about 4 when the temperature is raised by 10° C.
D)  Is no longer affected by the enzyme concentration at saturating substrate concentrations.
E)  Is virtually independent of the temperature, as long as heat denaturation is avoided.F) A) and B)
G) B) and D)

Question 7

Data are plotted for the action of a histone-modifying enzyme (solid lines)  in two graph formats in Figure 4.10.Dashed lines indicate the data for the enzyme in the presence of an effector molecule, deoxycytidine triphosphate (dCTP) .  Which statement is not true regarding this enzyme, its substrate (histone protein) , and its effector dCTP?

Accepted Answer

A)  The effector dCTP increases the Km.
B)  The enzyme is under allosteric control.
C)  The influence of the effector is reduced at high substrate (histone)  concentrations.
D)  The enzyme obeys Michaelis-Menten kinetics.
E)  dCTP is an inhibitory effector of enzyme activity.F) C) and D)
G) B) and E)

Question 8

The enzyme that catalyzes the following reaction (where ADP = adenosine diphosphate)  belongs to which broad enzyme class? Protein + ATP → Phosphoprotein + ADP

Accepted Answer

A)  Isomerase.
B)  Lyase.
C)  Oxidoreductase.
D)  Transferase.
E)  Ligase.F) A) and C)
G) B) and E)

Question 9

Which of the following is characteristic for the active sites of enzymes?

Accepted Answer

A)  Nearly all amino acid side chains of the protein participate in catalysis.
B)  The amino acid residues that form the active site are adjacent in the primary structure of the polypeptide.
C)  The amino acid residues in the active site that bind the substrate are always the ones that catalyze the reaction.
D)  In many cases, the active site changes its conformation when the substrate binds.
E)  In many cases, the initial binding of the substrate to the active site involves the formation of a covalent bond.F) A) and B)
G) None of the above

Question 10

Racemase enzymes interconvert:

Accepted Answer

A)  Epimers.
B)  Anomers.
C)  Enantiomers.
D)  Diasteriomers.
E)  Aldoses and ketoses.F) A) and B)
G) A) and C) C

Question 11

The "catalytic triad" in the active site of the serine protease thrombin contains the three amino acids:

Accepted Answer

A)  Aspartate, glutamate, histidine.
B)  Cysteine, arginine, serine.
C)  Glutamate, histidine, tryptophan.
D)  Serine, histidine, aspartate.
E)  Threonine, asparagine, tyrosine.F) B) and E)
G) B) and C)

Question 12

A cold virus produces an enzyme rhinase, which is acted upon by a drug called rhinex.Rhinex is known to be a noncompetitive inhibitor of the viral enzyme.Which of the dashed lines in Figure 4.8 describes the action of the enzyme in the presence of drug? The solid line describes the action of the drug-free enzyme.

Accepted Answer

A)  I.
B)  II.
C)  III.
D)  IV.
E)  V.F) A) and B)
G) A) and E)

Question 13

Alanine transaminase is a liver enzyme important in assessment of liver function.Figure 4.12 shows the "V vs.[S]" curve for the normal enzyme (solid line)  and the same enzyme in the presence of the enzyme inhibitor 2-aminobutanoic acid (dashed line) .  Which is true regarding the inhibitor 2-aminobutanoic acid?

Accepted Answer

A)  It is a noncompetitive inhibitor.
B)  It is an uncompetitive inhibitor.
C)  It is a positive allosteric effector that binds outside the active site.
D)  It is a competitive inhibitor.
E)  It is an irreversible (suicide)  inhibitor.F) None of the above
G) C) and D) D

Question 14

Tadalafil (Cialis)  is a competitive inhibitor of phosphodiesterase type 5.As a competitive inhibitor, you can expect tadalafil to:

Accepted Answer

A)  Covalently modify the enzyme.
B)  Bind to allosteric sites on the enzyme.
C)  Lower the Vmax of the reaction.
D)  Increase the Km of the enzyme for the substrate.
E)  Reduce the free energy of activation for the reaction.F) C) and E)
G) A) and E)

Question 15

Two different subtypes of matrix metalloproteinase, enzymes MMP-2 and MMP-9, are released from a squamous cell carcinoma.The enzymes behave according to Michaelis-Menten kinetics by the measured parameters in the table, in the same substrate: 
Оn the basis of these data, which of the following is a true statement?

Accepted Answer

A)  MMP-2 makes more product than MMP-9 at the same enzyme concentrations.
B)  MMP-2 is more stable to proteolytic degradation than MMP-9.
C)  MMP-2 is denatured in the extracellular environment faster than MMP-9.
D)  MMP-2 is more active at its maximal velocity than MMP-9.
E)  MMP-2 reaches half-maximal velocity at a higher substrate concentration than does MMP-9.F) A) and D)
G) A) and C)

Question 16

Which is true for enzymes in general?

Accepted Answer

A)  They reduce the free energy of the product in relation to that of the substrate.
B)  They can catalyze their reaction over a wide pH range.
C)  They increase the rate of the forward and backward reactions in proportion.
D)  When the substrate is chiral, both isomeric forms can be used as substrates of the enzymatic reaction.
E)  They alter the position of the equilibrium for a reaction.F) A) and B)
G) D) and E)

Question 17

Aldehyde groups are present in some metabolites.These aldehyde groups are most likely to be metabolized with the help of which type of enzyme?

Accepted Answer

A)  Monooxygenase.
B)  Dehydrogenase.
C)  Kinase.
D)  Synthetase.
E)  Hydrolase.F) A) and D)
G) A) and C) B

Question 18

The term ligase refers to a class of enzymes that catalyzes:

Accepted Answer

A)  Hydrogen transfer reactions.
B)  The transfer of a functional group from one molecule to another.
C)  The removal of a group, forming a C=C double bond in the substrate.
D)  The joining together of two molecules.
E)  Cleavage of a bond.F) A) and E)
G) A) and D)

Question 19

Thiol proteases cleave peptide bonds by a mechanism similar to that of serine proteases, such as trypsin and chymotrypsin, but they contain cysteine instead of serine.In which way does the sulfhydryl group of cysteine participate in the reaction?

Accepted Answer

A)  It participates in substrate binding and thereby helps determine the substrate specificity of the enzyme.
B)  It reacts covalently with the side chain of an acidic amino acid residue in the substrate.
C)  It attacks the C=O portion of a peptide bond and forms a thioester with it.
D)  It relays electrons to the peptide bond of the substrate, thereby facilitating the formation of a tetrahedral intermediate.
E)  It forms a transient disulfide bond with a cysteine side chain of the substrate.F) None of the above
G) A) and B)

Question 20

A liver enzyme called two-substrate inactivates a drug by the following reaction, where NADP is nicotinamide adenine dinucleotide phosphate and NADPH is the reduced form of NADP: Drug + NADPH ? Inactive product + NADP⁺
The Km and physiological substrate concentrations (both in millimoles per liter)  are given in the table for both substrates. 
What is the rate-limiting substrate under these conditions, and what is the derived Michaelis-Menten equation that describes the velocity of product formation by the enzyme?

Accepted Answer

A)  Drug limiting; vo = Vmax.
B)  NADPH limiting; 1/2 Vmax.
C)  NADPH limiting; (Vmax x [NADPH]) /0.22 mmol.
D)  Drug limiting; (Vmax x [Drug]) /0.12 mmol.
E)  NADPH limiting; k2/Km.F) D) and E)
G) A) and D)

Exam 4: Enzymatic Reactions

In which way is the transition state of an enzyme-catalyzed reaction different from the transition state of the corresponding uncatalyzed reaction?

Correct Answer
verified

Neviripine is a drug for human immunodeficiency virus (HIV) infection that is a noncompetitive inhibitor of reverse transcriptase.As a noncompetitive inhibitor, it:

Correct Answer
verified

Correct Answer
verified

The maximal reaction rate (Vmₐₓ) is a kinetic property of an enzymatic reaction that depends on the incubation conditions, the enzyme concentration, and:

Correct Answer
verified

Most NAD-using enzymes are named as:

Correct Answer
verified

The rate of a typical enzyme-catalyzed reaction:

Correct Answer
verified

Correct Answer
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The enzyme that catalyzes the following reaction (where ADP = adenosine diphosphate) belongs to which broad enzyme class? Protein + ATP → Phosphoprotein + ADP

Correct Answer
verified

Which of the following is characteristic for the active sites of enzymes?

Correct Answer
verified

Racemase enzymes interconvert:

Correct Answer
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C

The "catalytic triad" in the active site of the serine protease thrombin contains the three amino acids:

Correct Answer
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Correct Answer
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Correct Answer
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D

Tadalafil (Cialis) is a competitive inhibitor of phosphodiesterase type 5.As a competitive inhibitor, you can expect tadalafil to:

Correct Answer
verified

Correct Answer
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Which is true for enzymes in general?

Correct Answer
verified

Aldehyde groups are present in some metabolites.These aldehyde groups are most likely to be metabolized with the help of which type of enzyme?

Correct Answer
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B

The term ligase refers to a class of enzymes that catalyzes:

Correct Answer
verified

Thiol proteases cleave peptide bonds by a mechanism similar to that of serine proteases, such as trypsin and chymotrypsin, but they contain cysteine instead of serine.In which way does the sulfhydryl group of cysteine participate in the reaction?

Correct Answer
verified

Correct Answer
verified

Exam 4: Enzymatic Reactions

In which way is the transition state of an enzyme-catalyzed reaction different from the transition state of the corresponding uncatalyzed reaction?

Correct AnswerverifiedShow Answer

Neviripine is a drug for human immunodeficiency virus (HIV) infection that is a noncompetitive inhibitor of reverse transcriptase.As a noncompetitive inhibitor, it:

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

The maximal reaction rate (Vmₐₓ) is a kinetic property of an enzymatic reaction that depends on the incubation conditions, the enzyme concentration, and:

Correct AnswerverifiedShow Answer

Most NAD-using enzymes are named as:

Correct AnswerverifiedShow Answer

The rate of a typical enzyme-catalyzed reaction:

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

The enzyme that catalyzes the following reaction (where ADP = adenosine diphosphate) belongs to which broad enzyme class? Protein + ATP → Phosphoprotein + ADP

Correct AnswerverifiedShow Answer

Which of the following is characteristic for the active sites of enzymes?

Correct AnswerverifiedShow Answer

Racemase enzymes interconvert:

Correct AnswerverifiedC

The "catalytic triad" in the active site of the serine protease thrombin contains the three amino acids:

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Correct AnswerverifiedD

Tadalafil (Cialis) is a competitive inhibitor of phosphodiesterase type 5.As a competitive inhibitor, you can expect tadalafil to:

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

Which is true for enzymes in general?

Correct AnswerverifiedShow Answer

Aldehyde groups are present in some metabolites.These aldehyde groups are most likely to be metabolized with the help of which type of enzyme?

Correct AnswerverifiedB

The term ligase refers to a class of enzymes that catalyzes:

Correct AnswerverifiedShow Answer

Thiol proteases cleave peptide bonds by a mechanism similar to that of serine proteases, such as trypsin and chymotrypsin, but they contain cysteine instead of serine.In which way does the sulfhydryl group of cysteine participate in the reaction?

Correct AnswerverifiedShow Answer

Correct AnswerverifiedShow Answer

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Correct Answer
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C

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D

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B

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