Essential Biochemistry 3rd Edition by Charlotte W. Pratt – Kathleen Cornely – Test bank

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Essential Biochemistry 3rd Edition by Charlotte W. Pratt – Kathleen Cornely – Test bank

 

Sample  Questions

 

Package Title: Pratt & Cornely Test Bank

Course Title: Pratt & Cornely

Chapter Number: 6

 

 

Question type: Multiple Choice

 

 

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

 

  1. A) transferases
  2. B) isomerases
  3. C) allosteric enzymes
  4. D) holoenzymes
  5. E) isozymes

 

Answer:  E

 

Difficulty:  Easy

Section Reference:  6-1

Learning Objective:  Explain how enzymes differ from other catalysts

 

2) An uncatalyzed reaction has a rate of 4.2 x 10–7 sec–1.  When an enzyme is added the rate is 3.2 x 104 sec–1.  Calculate the rate enhancement caused by the enzyme.

 

  1. A) 6 x 1010
  2. B) 2 x 104
  3. C) 3 x 10–2
  4. D) 4 x 10–3
  5. E) cannot be determined

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  6-1

Learning Objective:  Explain how enzymes differ from other catalysts

 

 

3) Which of the following is the most effective way to increase the rate of a biochemical reaction?

 

  1. A) increase the temperature
  2. B) increase the concentrations of the reactants
  3. C) increase or decrease the pH
  4. D) add a catalyst
  5. E) none of the above

 

Answer:  D

 

Difficulty:  Easy

Section Reference:  6-1

Learning Objective:  Explain how enzymes differ from other catalysts

 

 

4) Chymotrypsin catalyzes the hydrolysis of a peptide bond and is therefore categorized as a _____.

 

  1. A) oxidoreductase
  2. B) transferase
  3. C) hydrolase
  4. D) lyase
  5. E) ligase

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  6-1

Learning Objective:  Explain how enzymes differ from other catalysts

 

 

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

 

  1. A) natural selection
  2. B) specificity
  3. C) high affinity
  4. D) processivity
  5. E) none of the above

 

Answer:  B

 

Difficulty:  Easy

Section Reference:  6-1

Learning Objective:  Explain how enzymes differ from other catalysts

 

 

6) The highest point in a reaction coordinate diagram represents _____.

 

  1. A) an intermediate of the reaction pathway
  2. B) the reactants in an exergonic reaction
  3. C) the products in an endergonic reaction
  4. D) the transition state
  5. E) the overall DG for the reaction

 

Answer:  D

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

7) How does a catalyst affect the overall DG of an endergonic reaction?

 

  1. A) it has no effect
  2. B) the reaction becomes more endergonic
  3. C) the reaction has a DG of zero
  4. D) the reaction becomes exergonic
  5. E) none of the above

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

8) How does a catalyst increase the rate of a reaction?

 

  1. A) it makes the reaction more exergonic
  2. B) it increases the temperature of the reaction
  3. C) it allows reacting molecules to more easily form the transition state
  4. D) it causes a localized increase in the concentration of reactants
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

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

 

  1. A) cofactor
  2. B) metal ion
  3. C) coenzyme
  4. D) cosubstrate
  5. E) prosthetic group

 

Answer:  E

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

10) An enzyme that forms a covalent bond with its substrate during the course of a reaction is considered to undergo _____.

 

  1. A) acid-base catalysis
  2. B) covalent catalysis
  3. C) electrophilic catalysis
  4. D) metal ion catalysis
  5. E) none of the above

 

Answer:  B

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

11) Which of the following amino acids would be most likely found in the active site of an enzyme that uses acid-base catalysis?

 

  1. A) Asn
  2. B) Ser
  3. C) Met
  4. D) His
  5. E) Trp

 

Answer:  D

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

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

 

  1. A) an intermediate
  2. B) two distinct transition states
  3. C) reactants that are lower in energy than an intermediate
  4. D) products that are lower in energy than an intermediate
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

13) 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.

 

  1. A) Arg
  2. B) Asn
  3. C) Lys
  4. D) Glu
  5. E) Ser

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

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

 

  1. A) Na+
  2. B) Zn2+
  3. C) Ag+
  4. D) K+
  5. E) Ba2+

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

15) 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?

 

  1. A) transition metal cation
  2. B) Asp residue
  3. C) Gln residue
  4. D) transition metal anion
  5. E) none of the above

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

16) What three amino acids are found in the catalytic triad of chymotrypsin?

 

  1. A) Glu, His, Thr
  2. B) Ser, Arg, Cys
  3. C) Asp, His, Ser
  4. D) Cys, Lys, Glu
  5. E) Asn, His, Thr

 

Answer:  C

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

17) What amino acid performs the nucleophilic attack during the chymotrypsin mechanism?

 

  1. A) Ser
  2. B) His
  3. C) Lys
  4. D) Cys
  5. E) Thr

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

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

 

  1. A) general acid only
  2. B) general base only
  3. C) general acid then general base
  4. D) general base then general acid
  5. E) nucleophile

 

Answer:  D

 

Difficulty:  Hard

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

19) If the Asp in the chymotrypsin active site was mutated to another amino acid, which of the following would be considered an invisible mutation in that it is least likely to impact the function of the enzyme?

 

  1. A) Asp ® Asn
  2. B) Asp ® Glu
  3. C) Asp ® His
  4. D) Asp ® Ser
  5. E) Asp ® Lys

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  6-2

Learning Objective:  List the chemical mechanisms enzymes use to accelerate reactions

 

 

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

 

  1. A) substrates
  2. B) products
  3. C) transition states
  4. D) intermediates
  5. E) all are bound very tightly

 

Answer:  C

 

Difficulty:  Easy

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

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

 

  1. A) hydrogen bonding between the enzyme and the anion from the carbonyl oxygen
  2. B) electrostatic interaction of the positively charged His and carbonyl oxygen
  3. C) electrostatic interaction of the negatively charged Asp and carbonyl oxygen
  4. D) electrostatic interaction of the active site Zn2+ and carbonyl oxygen
  5. E) all of the above

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

22) 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?

 

  1. A) 11-fold increase
  2. B) 37-fold increase
  3. C) 60-fold increase
  4. D) 100-fold increase
  5. E) 1011-fold increase

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

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

 

  1. A) dipole-dipole interaction
  2. B) electrostatic interaction
  3. C) hydrogen bond
  4. D) low-barrier hydrogen bond
  5. E) covalent bond

 

Answer:  D

 

Difficulty:  Medium

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

24) The ability for an enzyme to change its shape upon substrate binding represents the concept of _____.

 

  1. A) lock and key
  2. B) induced fit
  3. C) proximity and orientation effects
  4. D) covalent catalysis
  5. E) none of the above

 

Answer:  B

 

Difficulty:  Easy

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

25) 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?

 

  1. A) electrostatic catalysis
  2. B) desolvation catalysis
  3. C) non-aqueous catalysis
  4. D) hydrogen-bonded catalysis
  5. E) closed-system catalysis

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

26) Chymotrypsin catalyzes the hydrolysis of peptide bonds adjacent to _____ residues in a peptide.

 

  1. A) neutral polar
  2. B) nonpolar
  3. C) negatively charged
  4. D) positively charged
  5. E) all of the above since chymotrypsin has little substrate specificity

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  6-3

Learning Objective:  Describe how enzymes stabilize transition states

 

 

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

 

  1. A) Ser
  2. B) His
  3. C) Lys
  4. D) Val
  5. E) Asp

 

Answer:  E

 

Difficulty:  Easy

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

28) 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?

 

  1. A) Trp ® Ser
  2. B) Leu ® Ala
  3. C) Gly ® Val
  4. D) Lys ® Asp
  5. E) Val ® Asn

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

29) The molecule chymotrypsinogen is known as a(n) _____.

 

  1. A) apoenzyme
  2. B) holoenzyme
  3. C) protease inhibitor
  4. D) zymogen
  5. E) none of the above

 

Answer:  D

 

Difficulty:  Easy

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

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

 

  1. A) thrombin
  2. B) factor X
  3. C) factor VII
  4. D) factor VIIa
  5. E) prothrombin

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

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

 

  1. A) reversible; reversible
  2. B) irreversible; reversible
  3. C) reversible; irreversible
  4. D) irreversible; irreversible
  5. E) none of the above since antithrombin is not an inhibitor of thrombin

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

32) Which of the following is true regarding heparin?

 

  1. A) it is an allosteric activator of antithrombin
  2. B) it is a sulfated polysaccharide
  3. C) it simultaneously binds to antithrombin and the target of antithrombin
  4. D) it is used clinically as an anticoagulant
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

33) Zymogens are not enzymatically active because _____.

 

  1. A) they do not contain the cofactors required for catalysis
  2. B) they are the product of mutated genes
  3. C) their active sites are distorted and incapable of enzymatic activity
  4. D) the pH of their environment is not optimal for activity
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

 

34) Which of the following is a feature of protease inhibitor specific for trypsin?

 

  1. A) contains a positive charge to mimic the charge of the substrate
  2. B) ability to interact with the Ser of the catalytic triad
  3. C) inability to form the tetrahedral intermediate
  4. D) high affinity for the enzyme active site
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  6-4

Learning Objective:  Explain how enzymes may be activated and inhibited

 

Package Title: Pratt & Cornely Test Bank

Course Title: Pratt & Cornely

Chapter Number: 7

 

 

Question type: Multiple Choice

 

 

1) Which of the following is true about enzymes?

 

  1. A) enzymes show very little specificity for their substrates
  2. B) enzymes catalyze reactions in only one direction
  3. C) enzyme activities can often be regulated
  4. D) enzymes reaction rates are generally slower than other chemical catalysts
  5. E) enzymes operate under a wide range of temperatures and pH

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  7-1

Learning Objective:  Explain why an enzyme’s activity varies with substrate concentration

 

 

2) A plot of velocity versus substrate concentration for a simple enzyme-catalyzed reaction produces a _____.  This indicates that at some point, the enzyme is _____.

 

  1. A) straight line; inhibited by product
  2. B) hyperbolic curve; saturated with substrate
  3. C) sigmoidal curve; inhibited by substrate
  4. D) hyperbolic curve; activated by substrate
  5. E) sigmoidal curve; saturated with substrate

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-1

Learning Objective:  Explain why an enzyme’s activity varies with substrate concentration

 

 

3) When a substrate and enzyme interact, the first chemical species formed is _____.

 

  1. A) enzyme-substrate complex
  2. B) enzyme-transition state complex
  3. C) enzyme-product complex
  4. D) enzyme plus product
  5. E) none of the above

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  7-1

Learning Objective:  Explain why an enzyme’s activity varies with substrate concentration

 

 

4) How is an enzyme-catalyzed reaction affected by the addition of more enzyme?

 

  1. A) velocity is not effected
  2. B) velocity will increase only if more substrate is also added
  3. C) velocity will increase
  4. D) velocity will decrease
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Easy

Section Reference:  7-1

Learning Objective:  Explain why an enzyme’s activity varies with substrate concentration

 

 

5) For a reaction A + B → C, if [B] is much larger than [A] so that [B] essentially remains constant over the course of the reaction, the kinetics will be _____.

 

  1. A) zero-order
  2. B) hyperbolic
  3. C) first-order
  4. D) sigmoidal
  5. E) pseudo first-order

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

6) Which of the following expresses the velocity for an enzyme-catalyzed reaction that obeys Michaelis-Menten kinetics?

 

  1. A) v = k1[E][S]
  2. B) v = k1[E][S] – k-1[ES]
  3. C) v = k1[E][S] + k2[ES]
  4. D) v = k2[ES]
  5. E) v = k2[ES] – k-1[ES]

 

Answer:  D

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

7) Which of the following must be true if the steady state assumption is to be used?

 

  1. A) [E]T = [ES]
  2. B) (k2k-1) / k1 = 1
  3. C) k1[E][S] = k2[ES]
  4. D) k1[E][S] = k2[ES] – k-1[ES]
  5. E) d[ES] / dt = 0

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

8) The Michaelis constant is defined as _____.

 

  1. A) KM = k2 / k1
  2. B) KM = (k2 + k-1) / k1
  3. C) KM = (k2k-1) / k1
  4. D) KM = (k2 + k1) / k-1
  5. E) KM = (k2k1) / k-1

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

9) Which of the following properly expresses the Michaelis-Menten equation?

 

  1. A) vo = Vmax [S] / (KM + [S])
  2. B) vo = Vmax KM / (KM + [S])
  3. C) kcat = Vmax / [E]T
  4. D) Vmax = vo [S] / (KM + [S])
  5. E) Vmax = vo KM / (KM + [S])

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

10) When is KM considered to be the same as the dissociation constant for the ES complex i.e., KM » [E] [S] / [ES].

 

  1. A) ES → E + P is fast compared to ES → E + S
  2. B) the turnover number is very large
  3. C) kcat/KM is near the diffusion-controlled limit
  4. D) k2 << k-1
  5. E) KM can never be the same as the dissociation constant

 

Answer:  D

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

11) What percentage of Vmax is obtained when the substrate is present at ¼ of the KM?

`

  1. A) 5%
  2. B) 20%
  3. C) 25%
  4. D) 80%
  5. E) 100%

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

12) If an enzyme-catalyzed reaction has a velocity of 2 mM/min and a Vmax of 10 mM/min when the substrate concentration is 0.5 mM, what is the KM?

 

  1. A) 0.2 mM
  2. B) 0.5 mM
  3. C) 1 mM
  4. D) 2 mM
  5. E) 5 mM

 

Answer:  D

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

13) Which of the following must be true for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity?

 

  1. A) [S] must be ¾KM
  2. B) [S] must be 1.5KM
  3. C) [S] must be 2KM
  4. D) [S] must be 3KM
  5. E) [S] must be 4KM

 

Answer: D

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

14) If an enzyme-catalyzed reaction with a KM of 3.5 mM has a velocity of 5 mM/min at a substrate concentration of 0.5 mM, what is the Vmax?

 

  1. A) 0.625 mM/min
  2. B) 15 mM/min
  3. C) 17.5 mM/min
  4. D) 35 mM/min
  5. E) 40 mM/min

 

Answer:  E

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

15) What is the kcat for a reaction in which Vmax is 0.4 mmoles/min and the reaction mixture contains 5 ´ 10-6 micromoles of enzyme?

 

  1. A) 2 x 10-14 min-1
  2. B) 2 x 10-11 min-1
  3. C) 8 x 107 min-1
  4. D) 4 x 108 min-1
  5. E) 8 x 109 min-1

 

Answer:  C

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

16) The catalytic constant, or kcat, is also known as the _____.

 

  1. A) turnover number
  2. B) saturation number
  3. C) catalytic efficiency number
  4. D) diffusion number
  5. E) Menten number

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

17) Which of the following indicates that an enzyme has evolved to its most efficient form?

 

  1. A) kcat is a large number
  2. B) KM is a small number
  3. C) KM is a large number
  4. D) kcat/KM is a small number
  5. E) kcat/KM is near the diffusion-controlled limit

 

Answer:  E

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

18) An extremely efficient enzyme has a _____ KM and a _____ kcat.

 

  1. A) small; small
  2. B) small; large
  3. C) large; large
  4. D) large; small
  5. E) kcat and KM do nothing to predict the efficiency of an enzyme

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

19) A Lineweaver-Burk plot is a _____.

 

  1. A) double reciprocal plot
  2. B) Michaelis-Menten plot
  3. C) sigmoidal plot
  4. D) hyperbolic plot
  5. E) logarithmic plot

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

20) If a Lineweaver-Burk plot gave a line with an equation of y = 0.490 x + 0.059, what is the velocity at a substrate concentration of 5 mM?  The original units for substrate were in mM and velocity in mM/s.

 

  1. A) 0.288 mM/s
  2. B) 0.399 mM/s
  3. C) 2.51 mM/s
  4. D) 6.37 mM/s
  5. E) the velocity cannot be determined from this data

 

Answer:  D

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

21) If a Lineweaver-Burk plot gave a line with an equation of y = 0.25 x + 0.34, what are the values of KM and Vmax if the substrate concentration is in mM and the velocity in mM/s?

 

  1. A) 0.085 mM and 0.34 mM/s
  2. B) 2.9 mM and 0.023 mM/s
  3. C) 0.74 mM and 2.9 mM/s
  4. D) 0.37 mM and 1.4 mM/s
  5. E) 1.35 mM and .034 mM/s

 

Answer:  C

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

22) Which of the following types of enzyme-catalyzed reactions follows non-Michaelis-Menten kinetics?

 

  1. A) bisubstrate reactions with a random mechanism
  2. B) bisubstrate reactions with a ping pong mechanism
  3. C) bisubstrate reactions with an ordered mechanism
  4. D) allosteric enzyme reactions
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Easy

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

23) In a bisubstrate reaction, reactant A binds, followed by reactant B which then get converted to products C and D.  An experiment showed that B cannot bind without A having bound first.  What mechanism is indicated by this data?

 

  1. A) ordered mechanism
  2. B) random mechanism
  3. C) ping pong mechanism
  4. D) cooperative mechanism
  5. E) none of the above

 

Answer:  A

 

Difficulty:  Medium

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

24) In a bisubstrate reaction, reactant A binds and is then converted to product C.  Next, reactant B binds and is then converted to product D.  An experiment showed that B cannot bind without C being released first.  What mechanism is indicated by this data?

 

  1. A) ordered mechanism
  2. B) random mechanism
  3. C) ping pong mechanism
  4. D) cooperative mechanism
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Hard

Section Reference:  7-2

Learning Objective:  Define the terms of the Michaelis–Menten equation

 

 

25) Some irreversible inhibitors are called _____ because they bind to the active site of the enzyme and begin the catalytic process, just like a normal substrate.

 

  1. A) irreversible substrates
  2. B) suicide substrates
  3. C) noncompetitive substrates
  4. D) ping pong substrates
  5. E) allosteric substrates

 

Answer:  B

 

Difficulty:  Easy

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

26) An inhibitor that binds to the active site only in the absence of the substrate and in a reversible fashion is a(n) _____.

 

  1. A) allosteric inhibitor
  2. B) suicide substrate
  3. C) mixed inhibitor
  4. D) noncompetitive inhibitor
  5. E) competitive inhibitor

 

Answer:  E

 

Difficulty:  Easy

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

27) How are the kinetics of an enzyme-catalyzed reaction affected by a competitive inhibitor?

 

  1. A) Vmax decreased, KM increased
  2. B) Vmax decreased, KM decreased
  3. C) Vmax decreased, KM unchanged
  4. D) Vmax unchanged, KM increased
  5. E) Vmax unchanged, KM decreased

 

Answer:  D

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

28) If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a competitive inhibitor present, what difference would be seen?

 

  1. A) the y-intercept would be lower for the inhibited reaction
  2. B) the y-intercept would be higher for the inhibited reaction
  3. C) the slope would be less for the inhibited reaction
  4. D) the slope would be greater for the inhibited reaction
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Hard

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

29) What type of inhibition explains why even at very high substrate concentrations, enzyme activity will decrease as time increases?

 

  1. A) allosteric inhibition
  2. B) product inhibition
  3. C) transition state analogs
  4. D) irreversible inhibition
  5. E) uncompetitive inhibition

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

30) What does the KI for a competitive inhibitor mean?

 

  1. A) higher KI values mean tighter binding to ES complex
  2. B) lower KI values mean tighter binding to ES complex
  3. C) higher KI values mean tighter binding to the enzyme
  4. D) lower KI values mean tighter binding to the enzyme
  5. E) KI values tell nothing about inhibitor binding

 

Answer:  D

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

31) Which of the following is true regarding transition state analogs?

 

  1. A) they are competitive inhibitors
  2. B) they bind to an active site with much higher affinity than most inhibitors
  3. C) they are much more stable than the transition state
  4. D) their affinity for an enzyme is often much greater that the substrate
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

32) A reversible inhibitor that binds to a site other than the active site regardless of whether or not the substrate is bound is a _____.

 

  1. A) noncompetitive inhibitor
  2. B) competitive inhibitor
  3. C) uncompetitive inhibitor
  4. D) allosteric inhibitor
  5. E) suicide substrate

 

Answer:  A

 

Difficulty:  Easy

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

33) How are the kinetics of an enzyme-catalyzed reaction affected by a purely noncompetitive inhibitor?

 

  1. A) Vmax decreased, KM increased
  2. B) Vmax decreased, KM decreased
  3. C) Vmax decreased, KM unchanged
  4. D) Vmax unchanged, KM increased
  5. E) Vmax unchanged, KM decreased

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

34) If a Lineweaver-Burk plot was made for an enzyme-catalyzed reaction, both with and without a noncompetitive inhibitor present, what difference would be seen?

 

  1. A) the y-intercept would be higher with slope unchanged for the inhibited reaction
  2. B) the y-intercept would be lower with larger slope for the inhibited reaction
  3. C) the y-intercept would be lower with smaller slope for the inhibited reaction
  4. D) the y-intercept would be higher with larger slope for the inhibited reaction
  5. E) the y-intercept would be higher with smaller slope for the inhibited reaction

 

Answer:  D

 

Difficulty:  Hard

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

35) How are the kinetics of an enzyme-catalyzed reaction affected by a mixed inhibitor?

 

  1. A) Vmax decreased, KM increased or decreased
  2. B) Vmax decreased, KM decreased
  3. C) Vmax decreased, KM increased
  4. D) Vmax unchanged, KM increased
  5. E) Vmax unchanged, KM increased or decreased

 

Answer:  A

 

Difficulty:  Hard

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

36) A reversible inhibitor that only affects multisubstrate enzymes and binds to the enzyme only after one substrate has bound is a _____.

 

  1. A) noncompetitive inhibitor
  2. B) uncompetitive inhibitor
  3. C) competitive inhibitor
  4. D) allosteric inhibitor
  5. E) suicide substrate

 

Answer:  B

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

37) Which of the following types of inhibition can be reversed by addition of more substrate?

 

  1. A) noncompetitive inhibition
  2. B) competitive inhibition
  3. C) uncompetitive inhibition
  4. D) irreversible inhibition
  5. E) none of the above

 

Answer:  B

 

Difficulty:  Easy

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

38) Which of the following statements regarding allosteric enzymes is true?

 

  1. A) they are always oligomeric
  2. B) they are generally found at regulatory sites in metabolic pathways
  3. C) they are subject to regulation by both positive and negative effectors
  4. D) a plot of velocity versus [substrate] often yields a sigmoidal curve
  5. E) all of the above

 

Answer:  E

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics

 

 

39) Which of the following represents a rapid and reversible mechanism to alter the activity of an enzyme?

 

  1. A) synthesis of more enzyme to increase activity
  2. B) degradation of enzyme to decrease activity
  3. C) covalent attachment of a phosphate group to increase or decrease activity
  4. D) movement of an enzyme from one cellular compartment to another
  5. E) none of the above

 

Answer:  C

 

Difficulty:  Medium

Section Reference:  7-3

Learning Objective:  Distinguish the effects of different types of enzyme inhibitors on enzyme kinetics