Deck 12: Enzyme Kinetics, Inhibition and Control

Question 1

In order for an enzymatic reaction obeying the Michaelis-Menten equation to reach 3/4 of its maximum velocity,

A)[S] would need to be equal to K_M
B)[S] would need to be ½ K_M
C)[S] would need to be 3K_M
D)[S] would need to be ¾ K_M
E)not enough information is given to make this calculation

Answer 1

[S] would need to be 3K_M

Question 2

Matching
Different enzymes that catalyze the same reaction, although may be found in different tissues, are known as ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Answer 2

isozymes

Question 3

Matching
The type of enzyme inhibition in which V_max is unaffected is ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Answer 3

Competitive inhibition

Question 4

Matching
A lead compound for a new drug should bind to its target protein with a very ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 5

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

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 6

Matching

-Assume a first order reaction, the rate of the reaction 2A $\rarr$ B is dependent on ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 7

Matching

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

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 8

K_M is

A)a measure of the catalytic efficiency of the enzyme.
B)equal to half of V_max
C)the rate constant for the reaction ES $\rightarrow$ E + P.
D)the [S] that half-saturates the enzyme.
E)a ratio of substrate concentration relative to catalytic power.

Question 9

For a reaction A + B $\rightarrow$ C, if the concentration of B is much larger than A so that [B] remains constant during the reaction while [A] is varied, the kinetics will be

A)sigmoidal.
B)pseudo-first-order.
C)unimolecular.
D)zero-order.
E)hyperbolic.

Question 10

Matching
In uncompetitive inhibition, the inhibitor binds only to the ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 11

The K_M can be considered to be the same as the dissociation constant K_S for E + S binding if

A)the concentration of [ES] is unchanged.
B)ES $\rightarrow$ E + P is fast compared to ES $\rightarrow$ E + S.
C)k₁ >> k₂
D)k₂ << k_-1.
E)this statement cannot be completed because K_M can never approximate K_S.

Question 12

Find k_cat for a reaction in which V_max is 4 × 10^-4 mol•min^-1 and the reaction mixture contains one microgram of enzyme (the molecular weight of the enzyme is 200,000D).

A)2 × 10^-11 min^-1
B)8 × 10⁷ min^-1
C)8 × 10⁹ min^-1
D)2 × 10^-14 min^-1

Question 13

Find the initial velocity for an enzymatic reaction when V_max = 6.5 × 10^-5 mol•sec^-1, [S] = 3.0 × 10^-3 M, K_M = 4.5 × 10^-3 M and the enzyme concentration at time zero is 1.5 × 10^-2 $\mu$ M.

A)3.9 × 10^-5 mol•sec^-1
B)2.6 × 10^-5 mol•sec^-1
C)1.4 × 10^-2 mol•sec^-1
D)8.7 × 10^-3 mol•sec^-1
E)Not enough information is given to make this calculation.

Question 14

Reaction that is first order with respect to A and B

A)is dependent on the concentration of A and B.
B)is dependent on the concentration of A.
C)has smaller rate constants than first-order reactions regardless of reactant concentration.
D)is independent of reactant concentration.
E)is always faster than first-order reactions due to loss of concentration dependence.

Question 15

A lead compound would be most promising if it had:

A)K_I = 4.7 × 10⁵ M.
B)K_I = 1.5 × 10⁸ M.
C)K_I = 1.5 × 10^-8 M.
D)K_I = 4.7 × 10^-5 M.
E)K_M = 4.7 × 10⁵ M.

Question 16

What is the velocity of a first-order reaction at 37^oC when the reactant concentration is 6 × 10^-2 M and the rate constant is 8 × 10³ sec^-1?

A)1.33 × 10⁵ M^-1•sec^-1
B)1.33 × 10⁵ M•sec
C)7.5 × 10^-2 M•sec
D)4.8 × 10² M•sec^-1
E)Not enough data are given to make this calculation

Question 17

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

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 18

An enzyme is near maximum efficiency when

A)its turnover number is near V_max.
B)k_cat/K_M is near 10⁸ M^-1s^-1.
C)k₁ << k_-1.
D)k_cat/K_M is equal to k_cat.
E)K_M is large when k₂ exceeds k₁.

Question 19

Matching
A two-substrate enzymatic reaction in which one product is produced before the second substrate binds to the enzyme has a ______ mechanism.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 20

Matching

-The E+S $\rarr$ E+P reaction is ______.

A)isozymes
B)[A]
C)the rate constant
D)Ping Pong
E)bimolecular
F)ES complex
G)random ordered
H)competitive inhibition
I)unimolecular
J)[A]²
K)Competitive inhibition
L)phosphorylation
M)small KS
N)large KS
O)uncompetitive inhibition
P)[B]

Question 21

Protein kinases are involved in

A)the digestion of drugs to potentially toxic byproducts.
B)the degradation of enzymes to the component amino acids.
C)the phosphorylation of a wide variety of proteins.
D)the metabolism of drugs to water soluble, excretable compounds.
E)all of the above

Question 22

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

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

Question 23

Learning objective: Reaction Kinetics
The following questions refer to the diagram (with boxes where it has been left incomplete):
Which of the following is correct in regards to the diagram above?

A)X=A, Y=B, Z=P
B)X=B, Y=A, Z=Q
C)X=E, Y=A, Z=E
D)X=E, Y=B, Z=Q
E)X=E, Y=B, Z=P

Question 24

________ clinical trials are focused on evaluating the efficacy of new drug candidates, and usually use _____ test.

A)Phase 1; single blind
B)Phase 1; double blind
C)Phase 2; single blind
D)Phase 2; double blind
E)Phase 3; double blind

Question 25

The following questions 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 26

[S] = K_M for a simple enzymatic reaction.When [S] is doubled the initial velocity is

A)2 V_max
B)equal to V_max
C)(1/3)V_max
D)0.5 V_max
E)2 K_M/[S]

Question 27

Irreversible enzyme inhibitors

A)inactivate the enzyme
B)inhibit competitively
C)maximize product by minimizing ES $\rarr$ E+S
D)behave allosterically
E)function via Ping Pong mechanism

Question 28

Learning objective: Reaction Kinetics
The following questions refer to the diagram (with boxes where it has been left incomplete):
A compound that distorts the active site, rendering the enzyme catalytically inactive is called

A)a uncompetitive inhibitor
B)an allosteric effector
C)an inactivator
D)a competitive inhibitor
E)none of the above

Question 29

Pseudo-first-order reaction kinetics would be observed for the reaction A + B $\rarr$ C

A)if [A] or [B] > [C].
B)if [C]>[A] and [C]>[B].
C)if [A] or [B] = 0.
D)if [C] = 0.
E)none of the above

Question 30

The catalytic efficiency of an enzyme can never exceed

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

Question 31

Fourth-order reactions.

A)have three or more sequential rate determining steps.
B)require a 'Ping Pong' mechanism.
C)are best analyzed using Lineweaver-Burk plots.
D)exist only when enzymatically catalyzed.
E)none of the above.

Question 32

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 33

A Lineweaver-Burk plot is also referred to as
I.a sigmoidal plot.
II.a linear plot.
III.a Michaelis-Menten plot.
IV.a double reciprocal plot.

A)II
B)II, III
C)IV
D)II, IV
E)III, IV

Question 34

Learning objective: Reaction Kinetics
The following questions refer to the diagram (with boxes where it has been left incomplete):
This diagram refers to a (an)

A)Ping Pong reaction.
B)ordered bisubstrate reaction.
C)random bisubstrate reaction.
D)double order ping pong reaction
E)X, Y, and Z must be provided in order to answer correctly

Question 35

The following questions refer to the overall transformation shown in the following reaction:
The Michaelis constant K_M is defined as
I.(k_-1 + k₂)/k₁
II.½ V_max
III.[S] = [ES]
IV.[ES]/2

A)I
B)I, II
C)II
D)I, IV
E)II, IV

Question 36

Allosteric activators

A)bind via covalent attachment.
B)stabilize conformations with higher K_s.
C)stabilize conformations with higher substrate affinity.
D)all of the above
E)none of the above.

Question 37

Parallel lines on a Lineweaver-Burk plot indicate
I.an increase in K_M.
II.decrease in K_M.
III.decrease in V_max.
IV.uncompetitive inhibition.

A)I, IV
B)II, III, IV
C)I or II, III
D)I or III, II
E)I, III, IV

Question 38

Enzyme activity in cells is controlled by which of the following?
I.covalent modifications
II.modulation of expression levels
III.feedback inhibition
IV.allosteric effectors

A)I
B)II
C)III
D)III, IV
E)I, II, III, IV

Question 39

The following questions 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 40

Compounds that function as "mixed inhibitors"
I.interfere with substrate binding to the enzyme.
II.bind to the enzyme reversibly.
III.can bind to the enzyme/substrate complex.

A)I
B)II
C)III
D)II, III
E)I, II, III

Question 41

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 42

In the plot below, can the K_M be determined? If so, what is its value?

A)Yes, it is 30 mM.
B)Yes, it is 30 mM/sec.
C)Yes, it is 60 mM/sec
D)Yes, it is 60 mM
E)No this data does not follow Michaelis-Menten kinetics

Question 43

K_M

A)is the concentration of substrate where the enzyme achieves ½ V_max.
B)is equal to Ks.
C)measures the stability of the product
D)is high if the enzyme has high affinity for the substrate.
E)All of the above are correct.

Question 44

The following data were collected under conditions indicated in the graph below during the time period of 0-5 seconds.Upon plotting the Lineweaver-Burk plot, the information given in the table below was determined.Based on this available information which of the following is FALSE?

A)The V_max equals 200 M/s
B)The Ks equals 500 M
C)The k_app equals 200 per second
D)The data was collected prior to reaching steady state.
E)The k_cat cannot be determined for this information.

Question 45

At substrate concentrations much lower than the enzyme concentration,

A)the rate of reaction is expected to be inversely proportional to substrate concentration.
B)the rate of reaction is expected to be directly proportional to substrate concentration.
C)first order enzyme kinetics are not observed.
D)the K_M is lower.
E)the rate of reaction is independent of substrate concentration.

Question 46

A new drug has been discovered which inhibits the reaction catalyzed by enzyme A.Based on the information shown below, what is this drug?

A)competitive inhibitor
B)uncompetitive inhibitor
C)mixed inhibitor
D)allosteric activator
E)More information is required to answer the question.

Question 47

Based on the figure in the question above (question 54), 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 48

A lab recently developed a new drug which is hypothesized to inhibit the enzyme cyclooxygenase-2 (COX-2)and reduce inflammation.In their first test they monitored the reaction of substrate as it is converted to product in the presence of the new drug (data shown below).If the hypothesis is correct the observed initial rate will be at least 2 times slower than the normal reaction without the drug.If the normal initial rate is 30 mM/s, does the data below indicate that the team has designed a successful inhibitor?

A)Yes.
B)No.
C)This cannot be determined with the information given.
D)The data is dependent on the maximal velocity.
E)The answer is dependent on the substrate concentration.

Question 49

Following several experiments, the data presented on the graph below was obtained.What can you determine from this graph?

A)This data may have been collected both in the absence (solid line)and presence (dashed line)of a competitive inhibitor.
B)This data may have been collected both in the absence (solid line)and presence (dashed line)of a mixed (noncompetitive)inhibitor.
C)This data may have been collected both in the absence (solid line)and presence (dashed line)of mechanism based inhibitor.
D)This data may have been collected both in the absence (solid line)and presence (dashed line)of an inhibitor which binds the active site.
E)More than one of the above are correct.

Question 50

From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the V_max?

A)0.24 μM/s
B)18 μM
C)0.2 μM
D)0.24 μM
E)0.12 μM/s

Question 51

The breakdown of dopamine is catalyzed by the enzyme monoamine oxidase (MAO).What is the final concentration of product if the starting dopamine concentration is 0.050 M and the reaction runs for 5 seconds.(Assume the rate constant for the reaction is 0.249 s⁻¹.)

A)0.050 M
B)0.014 M
C)0.018 M
D)1.2 M
E)0.025 M

Question 52

From the graph below plotting data that was collected under steady state conditions, velocity on the y-axis in units of μM/s and substrate concentration of the x-axis in units of μM, what is the K_M?

A)0.24 μM/s
B)18 μM
C)0.2 μM
D)0.24 μM
E)0.12 μM/s

Question 53

An extremely efficient enzyme called "efficase" catalyzes the conversion of "A" to "B." A researcher decides to mutate the enzyme in order to try to improve its performance.Following active site mutations, a significant reduction in the value of K_M and V_max was observed.Which of the following may have occurred?

A)The affinity of the enzyme for the substrate was increased to a point which did not favor propagation (continuation)of the reaction.
B)The decrease in V_max was not related to the decrease in K_M.
C)If the reaction was first-order, the change in K_M cannot have affected V_max.
D)The stability of E+S (E+A as written above)was increased, thereby increasing the K_M.
E)The reverse reaction (breakdown of EA to E+A)was favored, slowing the V_max.

Question 54

Enzyme E is responsible for conversion of substrate X to product U.As a result of this conversion electrons are transported to a coenzyme (FAD)within Enzyme E.In order for the reaction to be completed, a second substrate NAD⁺ must also bind Enzyme E and collect stored electrons (which converts it to product, NADH).The graph below shows the data while varying X, with fixed concentrations of NAD⁺.What type of multi-substrate mechanism does enzyme E utilize?

A)sequential - Ordered
B)sequential - Random
C)simultaneous addition
D)Ping Pong
E)Sequential but the data cannot differentiate between ordered and random.

Question 55

I propose to design a new drug which will act as an inhibitor for an enzyme.If I have used all current information about the mechanism of this enzyme to design this inhibitor and I carefully engineer it with similar chemical properties of the transition state, what type of inhibitor am I attempting to engineer and how will I know if I have succeeded?

A)A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in V_max.
B)A competitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in K_M.
C)A uncompetitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in K_M.
D)A uncompetitive inhibitor, collect kinetic data both in the presence and absence of inhibitor and watch for a change in V_max.
E)None of the above.