Deck 4: Proteins Iienzymes

Question 1

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

A) lock and key
B) induced fit
C) proximity and orientation effects
D) covalent catalysis
E) none of the above

Answer 1

induced fit

Question 2

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

A) oxidoreductase
B) transferase
C) hydrolase
D) lyase
E) ligase

Answer 2

hydrolase

Question 3

The highest point in a reaction coordinate diagram represents _____.

A) an intermediate of the reaction pathway
B) the reactants in an exergonic reaction
C) the products in an endergonic reaction
D) the transition state
E) the overall $\Delta$ G for the reaction

Answer 3

the transition state

Question 4

If A $\rightarrow$ B is a zero-order reaction, the rate is dependent on ______.

Question 5

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

A) straight line; inhibited by product
B) hyperbolic curve; saturated with substrate
C) sigmoidal curve; inhibited by substrate
D) hyperbolic curve; activated by substrate
E) sigmoidal curve; saturated with substrate

Question 6

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

A) enzyme-substrate complex
B) enzyme-transition state complex
C) enzyme-product complex
D) enzyme plus product
E) none of the above

Question 7

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

A) v = k₁[E][S]
B) v = k₁[E][S] - k_-1[ES]
C) v = k₁[E][S] + k₂[ES]
D) v = k₂[ES]
E) v = k₂[ES] - k_-1[ES]

Question 8

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

A) [E]_T = [ES]
B) (k₂ - k_-1) / k₁ = 1
C) k₁[E][S] = k₂[ES]
D) k₁[E][S] = k₂[ES] - k_-1[ES]
E) d[ES] / dt = 0

Question 9

The Michaelis constant is defined as _____.

A) K_M = k₂ / k₁
B) K_M = (k₂ + k_-1) / k₁
C) K_M = (k₂ - k_-1) / k₁
D) K_M = (k₂ + k₁) / k_-1
E) K_M = (k₂ - k₁) / k_-1

Question 10

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

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

Question 11

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

A) 0.625 mM/min
B) 15 mM/min
C) 17.5 mM/min
D) 35 mM/min
E) 40 mM/min

Question 12

When [S] = K_M, $\nu$ ₀ = (_____) × (V_max).

A) [S]
B) 0.75
C) 0.5
D) K_M
E) k_cat

Question 13

refer to the overall transformation shown in the following reaction:

-Which of the following is (are) true?

A) The [ES] will remain constant if k₂ > k₁ and k_-1 < k₂.
B) The reaction is zero order with respect to [S] if [S]>>[E]
C) It describes a double displacement reaction
D) All of the above are true.
E) None of the above is true.

Question 14

refer to the overall transformation shown in the following reaction:

-For the reaction, the steady state assumption _____.

A) implies that k₁ = k_-1
B) implies that k_-1 and k₂ are such that the [ES] = k1[ES]
C) [P]>>[E]
D) [S] = [P]
E) ES breakdown occurs at the same rate as ES formation

Question 15

A Lineweaver-Burk plot is a _____.

A) double reciprocal plot
B) Michaelis-Menten plot
C) sigmoidal plot
D) hyperbolic plot
E) logarithmic plot

Question 16

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.

A) 0.288 mM/s
B) 0.399 mM/s
C) 2.51 mM/s
D) 6.37 mM/s
E) the velocity cannot be determined from these data

Question 17

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

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

Question 18

Determine the K_M and V_max from the following graph. (Note: On the x-axis the minor tick mark spacing is 0.005; on the y-axis the minor tick mark spacing is 0.002)

A) K_M = [0.006]; V_max = 0.0075/s
B) K_M = [0.196]; V_max = 0.0075/s
C) K_M = [165]; V_max = 33/s
D) K_M = [33]; V_max = 167/s
E) K_M = [270]; V_max x = 68/s

Question 19

Based on the figures below, which of the following expressions would be correct?

A) V_max = 1/B
B) C = 1/V_max
C) D = V_max
D) D = 1/V_max
E) A = 1/V_max

Question 20

Based on the figure below, which of the following expressions would correctly define K_M?

A) A = K_M
B) K_M = A/2
C) B = K_M
D) C = -K_M
E) D= 1/K_M

Question 21

The catalytic constant, or k_cat, is also known as the _____.

A) turnover number
B) saturation number
C) catalytic efficiency number
D) diffusion number
E) Menten number

Question 22

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

A) k_cat is a large number
B) K_M is a small number
C) K_M is a large number
D) k_cat/K_M is a small number
E) k_cat/K_M is near the diffusion-controlled limit

Question 23

An extremely efficient enzyme has a _____ K_M and a _____ k_cat.

A) small; small
B) small; large
C) large; large
D) large; small
E) k_cat and K_M do nothing to predict the efficiency of an enzyme

Question 24

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.

A) irreversible substrates
B) suicide substrates
C) noncompetitive substrates
D) ping pong substrates
E) allosteric substrates

Question 25

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

A) allosteric inhibitor
B) suicide substrate
C) mixed inhibitor
D) noncompetitive inhibitor
E) competitive inhibitor

Question 26

What does the K_I for a competitive inhibitor mean?

A) Higher K_I values mean tighter binding to ES complex.
B) Lower K_I values mean tighter binding to ES complex.
C) Higher K_I values mean tighter binding to the enzyme.
D) Lower K_I values mean tighter binding to the enzyme.
E) K_I values tell nothing about inhibitor binding.

Question 27

A reversible inhibitor that binds to the enzyme only after one substrate has bound is a _____.

A) noncompetitive inhibitor
B) uncompetitive inhibitor
C) competitive inhibitor
D) allosteric inhibitor
E) suicide substrate

Question 28

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

A) noncompetitive inhibition
B) competitive inhibition
C) uncompetitive inhibition
D) irreversible inhibition
E) none of the above

Question 29

In ______, the inhibitor binds to a site involved in both substrate binding and catalysis.

Question 30

An enzyme that forms a covalent bond with its substrate during a reaction is considered to undergo _____.

A) acid-base catalysis
B) covalent catalysis
C) electrophilic catalysis
D) metal ion catalysis
E) none of the above

Question 31

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

A) Asn
B) Ser
C) Met
D) His
E) Trp

Question 32

Proton transfer from an acid, lowering the free energy of a reaction's transition state, is characteristic of _____.

A) electrostatic catalysis
B) nucleophilic catalysis
C) general base catalysis
D) general acid catalysis
E) concerted acid-base catalysis

Question 33

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

A) Glu, His, Thr
B) Ser, Arg, Cys
C) Asp, His, Ser
D) Cys, Lys, Glu
E) Asn, His, Thr

Question 34

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

A) Ser
B) His
C) Lys
D) Cys
E) Thr

Question 35

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 affect the function of the enzyme?

A) Asp $\rightarrow$ Asn
B) Asp $\rightarrow$ Glu
C) Asp $\rightarrow$ His
D) Asp $\rightarrow$ Ser
E) Asp $\rightarrow$ Lys

Question 36

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

A) neutral polar
B) nonpolar
C) negatively charged
D) positively charged
E) all of the above because chymotrypsin has little substrate specificity

Question 37

In the lysosome reaction, the carbohydrate substrate is in the _____ conformation providing a contribution of catalytic energy via the ____ distortion.

A) half-chair; electrostatic
B) chair; strain
C) boat; strain
D) boat; electrostatic
E) half-chair; strain

Question 38

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

A) apoenzyme
B) holoenzyme
C) protease inhibitor
D) zymogen
E) none of the above

Question 39

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

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

Question 40

A common type of covalent modification of regulatory enzymes involves _____ of serine residues.

Question 41

Which of the following statements regarding allosteric enzymes is true?

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