The Behavior of Proteins: Enzymes

Question 1

How much faster is a reaction with the fastest enzyme than without a catalyst?
a. About 10 times faster.
b. About 100 times faster.
c. About 1,000 times faster.
d. About 10,000 times faster.
e. About 1020 times faster.

Answer 1

e

Question 2

As catalysts, enzymes are
a. significantly less effective than nonenzymatic catalysts
b. slightly less effective than nonenzymatic catalysts
c. significantly more effective than nonenzymatic catalysts
d. slightly more effective than nonenzymatic catalysts
e. exactly the same as nonenzymatic catalysts

Answer 2

c

Question 3

The rate of a reaction depends on
a. the free energy change
b. the activation energy
c. the enthalpy change
d. the entropy change

Answer 3

b

Question 4

Enzymatic activity has an optimum temperature because
a. the component amino acids have varying melting points
b. the rate of reactions is thermodynamically controlled
c. the side chains of essential residues are chemically degraded at higher temperatures
d. raising the temperature speeds up the reaction until protein denaturation sets in
e. the organism dies beyond a certain temperature

Answer 4

d

Question 5

The main difference between a catalyzed and an uncatalyzed reaction is that
a. the activation energy of the catalyzed reaction is lower.
b. the catalyzed reaction has a more favorable free energy change.
c. the catalyzed reaction has a more favorable enthalpy change.
d. the catalyzed reaction has a more favorable entropy change.

Answer 5

a

Question 6

Which of the following is not true?
a. In thermodynamics, spontaneous does not mean instantaneous or even fast.
b. If a reaction is spontaneous then it has a negative ΔG.
c. Speed of a reaction is a kinetic parameter, not a thermodynamic one.
d. A reaction with a positive ΔG^0 can never happen

Answer 6

d

Question 7

What effect does a catalyst have on the ΔG° of a reaction?
a. A catalyst lowers the ΔG°.
b. A catalyst raises the ΔG°.
c. A catalyst has no effect on the ΔG°.
d. It depend on the specific catalyst.

Answer 7

c

Question 8

Which of the following is most directly related to the speed of a reaction?
a. The temperature
b. The ΔG^0 of the reaction
c. The ΔG of the reaction
d. The ΔG^0‡ of the reaction
e. None of these is correct.

Answer 8

d

Question 9

A rate constant is
a. the rate of a reaction at standard temperature and pressure.
b. the rate of a reaction at equilibrium.
c. a proportionality constant relating the rate of a reaction to the concentration(s) of the reactant(s).
d. a kind of transition state.

Answer 9

c

Question 10

The rate of a reaction is always dependent on the concentration(s) of the reactant(s).
a. True
b. False

Answer 10

b

Question 11

All catalysts work by lowering the activation energy for a reaction.
a. True
b. False

Answer 11

a

Question 12

The amount of energy released during a reaction tells nothing about the rate at which that reaction will occur.
a. True
b. False

Answer 12

a

Question 13

Thermodynamically favorable reactions all release energy.
a. True
b. False

Answer 13

a

Question 14

The sign of Gibb’s Free Energy is positive (“+”) when energy is released.
a. True
b. False

Answer 14

b

Question 15

Which of the following is true about lactate dehydrogenase (LDH)?
a. There are two types of subunits, H amd M, that combine to form 5 types of isozymes
b. An increase in H-based isozymes was once used to diagnose heart attacks
c. An increase in blood levels of LDH of any kind is indicative of some sort of problem
d. One type of LDH has only H subunits
e. All of the choices

Answer 15

e

Question 16

The order of a reaction can be determined from the balanced equation for the reaction.
a. True
b. False

Answer 16

b

Question 17

The kinetic order of a reaction
a. can be determined by inspection from the coefficients of the balanced equation
b. must be determined experimentally
c. always depends on the concentration of enzyme
d. never depends on concentrations of reactants

Answer 17

b

Question 18

Given the rate law, rate = k[A][B], the overall reaction order is
a. zero
b. one
c. two
d. cannot be determined

Answer 18

c

Question 19

First order kinetics means:
a. The rate of a reaction is independent of the amount of reactant measured.
b. The rate of the reaction varies directly with the amount of reactant measured.
c. The rate of the reaction varies with the square of the amount of the reactant measured.
d. More information is needed to answer this question.
e. None of these is correct.

Answer 19

b

Question 20

The active site of an enzyme
a. is frequently located in a cleft in the enzyme.
b. is the portion of the enzyme to which the substrate binds.
c. contains the reactive groups that catalyze the reaction.
d. all of these are correct

Answer 20

d

Question 21

The substrate will only bind to the enzyme when the shapes fit together rigidly.
a. True
b. False

Answer 21

b

Question 22

In the induced-fit model of substrate binding to enzymes
a. the substrate changes its conformation to fit the active site
b. the active site changes its conformation to fit the substrate
c. there is a conformational change in the enzyme when the substrate binds
d. there is aggregation of several enzyme molecules when the substrate binds

Answer 22

c

Question 23

The E-S complex often shows as a slight depression in the energy profile for the reaction.
a. True
b. False

Answer 23

a

Question 24

The active site of an enzyme is the place where the following happens:
a. The enzyme substrate complex forms here.
b. The catalytic reaction happens here.
c. Allosteric regulation of enzyme rate occurs here.
d. The enzyme-substrate complex forms and the reaction occurs at the active site.
e. All of these are correct

Answer 24

d

Question 25

Which of the following is implied by induced fit between the enzyme's active site and the substrate? a. The enzyme is a flexible molecule. b. An enzyme will work equally well with different substrates. c. An active site can bind to different substrates. d. The enzyme is a flexible molecule so different substrates can bind. e. All of these are correct

Answer 25

e

Question 26

Which of the following is true? a. The E-S complex often dissociates with no reaction taking place. b. The E-S complex must form before a reaction can take place c. Once the E-S complex forms, it can go on to form product or dissociate to E + S d. All of these are correct

Answer 26

d

Question 27

Which of the following is true about the enzyme chymotrypsin? a. The enzyme can cleave peptides. b. The enzyme can cleave esters. c. The enzyme only binds to aromatic substrates. d. The enzyme can cleave substrates which are not naturally occurring. e. All of these are correct

Answer 27

e

Question 28

The reaction catalyzed by aspartate transcarbamoylase is a. the first step in the synthesis of amino acids. b. the first step in the synthesis of fatty acids. c. the first step in the synthesis of CTP and UTP. d. is part of glycolysis.

Answer 28

c

Question 29

In the reaction catalyzed by chymotrypsin, a graph in which the rate is plotted against the concentration of substrate a. is sigmoidal, characteristic of an allosteric enzyme b. shows that cooperative kinetics are observed c. shows that the reaction is zero order d. is hyperbolic, characteristic of a nonallosteric enzyme

Answer 29

d

Question 30

In the reaction catalyzed by aspartate transcarbamoylase, a graph in which the rate is plotted against the concentration of substrate a. is sigmoidal, characteristic of an allosteric enzyme b. shows that noncooperative kinetics are observed c. shows that the reaction is zero order d. is hyperbolic, characteristic of a nonallosteric enzyme

Answer 30

a

Question 31

The Michaelis-Menten approach to describing the kinetics of an enzyme-catalyzed reaction makes which of the following assumptions about the conversion of product into substrate? a. The product binds reversibly to the enzyme in order to be converted into the substrate. b. The product is not converted to substrate to any appreciable extent. c. The product is converted to substrate following simple first order kinetics. d. The product is converted to substrate following simple second order kinetics.

Answer 31

b

Question 32

The initial rate of an enzymatic reaction is usually determined in order to assure that a. the enzyme is active b. there is no reverse reaction of product to the enzyme-substrate complex c. the substrate is not used up d. the experiment can be completed quickly

Answer 32

b

Question 33

According to the steady-state assumption a. the product concentration does not change significantly b. the substrate concentration is large and does not change significantly c. the concentration of enzyme-substrate complex remains constant with time d. the free enzyme concentration is always in great excess to the concentration of enzyme-substrate complex

Answer 33

c

Question 34

Most enzyme reactions display first order kinetics for the individual substrates when the substrate concentration is low. a. True b. False

Answer 34

a

Question 35

When the substrate concentration is low, an enzyme reaction a. will display zero-order kinetics. b. will display first-order kinetics. c. will display second-order kinetics. d. will denature and cease to function.

Answer 35

b

Question 36

When an enzyme is saturated with substrates, a. it will display zero-order kinetics. b. it will display first-order kinetics. c. it will display second-order kinetics. d. it will denature and cease to function.

Answer 36

a

Question 37

The Michaelis constant is a. related to the molecular weight of the enzyme b. a measure of the resistance of the enzyme to denaturation c. a reflection of the percentage of polar amino acids in the enzyme d. a rough measure of the affinity of the enzyme for the substrate

Answer 37

d

Question 38

The KM expression is equal to a. (k1 + k2) / k−1 b. (k−1 + k2) / k1 c. (k1 + k−1) / k2 d. k−1 / k1

Answer 38

b

Question 39

Which of the following are related for a given enzyme? a. Vmax, KM, and percentage of α-helix b. Vmax, kcat, and percentage of β-sheet c. Vmax, kcat, and turnover number d. Vmax, KM, and molecular weight e. None of these are related in any way

Answer 39

c

Question 40

The Michaelis constant is a. the rate constant for the formation of the substrate-enzyme (E-S) complex. b. the rate constant for the breakdown of the substrate-enzyme (E-S) complex to form free enzyme and substrate. c. the rate constant for the breakdown of the substrate-enzyme (E-S) complex to form free enzyme and product. d. a compilation of several rate constants for the reaction.

Answer 40

d

Question 41

The drug acetazolamide: a. Is used to help fight altitude sickness b. Was found to ruin the taste of carbonated beverages c. Does not affect the taste of non-carbonated liquors d. Causes its effect on taste by inhibiting carbonic anhydrase 4 e. All of these

Answer 41

e

Question 42

The substrate-enzyme (E-S) complex a. always proceeds to form the products rapidly. b. always breaks down to form free enzyme and substrate. c. always breaks down to form free enzyme and product. d. may break down to form free enzyme and substrate, or free enzyme and product.

Answer 42

d

Question 43

When an enzyme-catalyzed reaction has two substrates and substrate A must bind before substrate B, the mechanism is called a. a ping-pong mechanism b. a random mechanism c. an ordered mechanism d. a suicide mechanism e. none of these is true

Answer 43

c

Question 44

Which of the following is true concerning a ping-pong mechanism? a. Either substrate can bind first b. Either product can leave first c. One product leaves before the second substrate binds d. One product leaves before either substrate has bound e. none of these are true

Answer 44

c

Question 45

A Lineweaver-Burk plot is useful in the analysis of enzymatic reactions because a. it is easier to see whether points deviate from a straight line than from a curve b. it is not affected by the presence of inhibitors c. it can be used whether or not the enzyme displays Michaelis-Menten kinetics d. all of the above

Answer 45

a

Question 46

The steady state of an enzyme reaction is the following: a. The rate observed just after mixing the enzyme and substrate. b. The rate observed and Vmax. c. The rate of product formation. d. The state which exists when E-S complex is forming as fast as it is breaking down. e. The state which exists when substrate concentration equals KM.

Answer 46

d

Question 47

If the y-intercept of a Lineweaver-Burk plot = 1.91 (sec/millimole) and the slope = 75.3 L/sec, Vmax equals: a. 0.0254 millimoles per second. b. 0.523 millimoles per second. c. 5.23 millimoles per second. d. 39.4 millimoles per second. e. 75.3 millimoles per second.

Answer 47

b

Question 48

If the y-intercept of a Lineweaver-Burk plot = 1.91 (sec/millimole) and the slope = 75.3 L/sec, KM equals: a. 0.0254 millimolar (mM). b. 0.523 millimolar (mM). c. 5.23 millimolar (mM). d. 39.4 millimolar (mM). e. 75.3 millimolar (mM).

Answer 48

d

Question 49

The Michaelis constant determines the Vmax of an enzymatic reaction. a. True b. False

Answer 49

b

Question 50

It is important that at physiological conditions, enzymes work at Vmax. a. True b. False

Answer 50

b

Question 51

Which of the following statements regarding the Michaelis constant is false? a. It is similar to the affinity constant between the enzyme and substrate. b. The dimension for the Michaelis constant is concentration, such as molarity. c. The Michaelis constant determines the Vmax. d. It is the substrate concentration necessary to reach 1/2 Vmax.

Answer 51

c

Question 52

To study the nature of an enzyme, Vmax is not as good a measurement as the catalytic rate constant kcat because: a. The Vmax is not a true constant since it depends on the concentration of enzyme b. The Vmax cannot be measured c. The Vmax is only valid for allosteric enzymes d. none of these

Answer 52

a

Question 53

The KM of hexokinase for glucose = 0.15 mM and for fructose, KM = 1.5 mM. Which is the preferred substrate? a. Glucose. b. Fructose. c. Neither substrate is preferred over the other. d. You cannot tell from the data given. e. None of these answers is correct.

Answer 53

a

Question 54

Competitive inhibitors have this effect: a. Modifying the KM value. b. Changing the value for Vmax. c. Interfering with substrate binding. d. This type of inhibitor both changes the KM and interferes with substrate binding. e. All of these are correct.

Answer 54

d

Question 55

Which of the following inhibitors binds to the enzyme at a site other than the active site? a. competitive inhibitor b. noncompetitive inhibitor c. irreversible inhibitor d. all of these e. none of these

Answer 55

b

Question 56

Inhibitors can have the following effects on enzyme kinetics: a. Modifying the KM value. b. Changing the value for Vmax. c. Interfering with substrate binding. d. An inhibitor can change the KM and interfere with substrate binding. e. All of these are correct.

Answer 56

e

Question 57

The value of Vmax changes in a. competitive inhibition b. noncompetitive inhibition c. both forms of inhibition d. neither form of inhibition

Answer 57

b

Question 58

The fundamental difference between competitive and noncompetitive inhibition is a. the degree of cooperativity of the reaction b. the size of the active site of the enzyme c. the manner of binding of substrate to the enzyme d. the manner of binding of inhibitor to the enzyme

Answer 58

d

Question 59

Which of the following is more likely to inhibit regulatory subunits of an allosteric enzyme? a. A competitive inhibitor b. A non-competitive inhibitor c. An irreversible inhibitor d. All of these are equally likely to inhibit a regulatory subunit

Answer 59

b

Question 60

For competitive inhibition a. the value of KM decreases b. the value of Vmax decreases c. it is possible to overcome the effect of the inhibitor by increasing the concentration of substrate d. none of the above

Answer 60

c

Question 61

Irreversible inhibitors of enzymatic reactions a. bind to the enzyme only at low temperatures. b. affect only serine side chains. c. react with the enzyme to produce a protein that is not enzymatically active and from which the original enzyme cannot be regenerated. d. are bound to the enzyme by the lock-and-key mechanism.

Answer 61

c

Question 62

A noncompetitive inhibitor a. binds to the enzyme at a site other than the active site b. is structurally related to the substrate c. does not affect the value of Vmax d. decreases the value of KM

Answer 62

a

Question 63

What effect is seen on a Lineweaver-Burk graph when a competitive inhibitor is added? a. The y-intercept is changed, but not change the slope of the line. b. The slope of the line is changed, but not the y-intercept. c. Both the y-intercept and the slope of the line are changed. d. Neither the y-intercept not the slope of the line is changed.

Answer 63

b

Question 64

What effect is seen on a Lineweaver-Burk graph when a mixed-type inhibitor is added? a. The y-intercept is changed, but not change the slope of the line. b. The slope of the line is changed, but not the y-intercept. c. Both the y-intercept and the slope of the line are changed. d. Neither the y-intercept not the slope of the line is changed.

Answer 64

c

Question 65

Generally speaking, a competitive inhibitor and the substrate cannot both bind to the enzyme at the same time. a. True b. False

Answer 65

a

Question 66

What effect is seen on a Lineweaver-Burk graph when a non-competitive inhibitor is added? a. The y-intercept is changed, but not change the slope of the line. b. The slope of the line is changed, but not the y-intercept. c. Both the y-intercept and the slope of the line are changed. d. Neither the y-intercept not the slope of the line is changed.

Answer 66

a

Question 67

Non-competitive inhibitors have this effect: a. Modifying the KM value. b. Changing the value for Vmax. c. Interfering with substrate binding. d. This type of inhibitor both changes the Vmax and interferes with substrate binding. e. All of these are correct

Answer 67

b

Question 68

If an inhibitor changes the slope of the Lineweaver-Burk graph, but not the y-intercept, it is this type of inhibition: a. Competitive. b. Non-competitive. c. Mixed Inhibition (uncompetitive inhibition). d. You cannot tell from the data given. e. More than one answer is correct.

Answer 68

a

Question 69

If an inhibitor changes the slope of the Lineweaver-Burk graph, but not the x-intercept, it is this type of inhibition: a. Competitive. b. Non-competitive. c. Mixed Inhibition (uncompetitive inhibition). d. You cannot tell from the data given. e. More than one answer is correct.

Answer 69

b

Question 70

Which of the following diseases has not been successfully treated using the principles of enzyme inhibition? a. AIDS. b. Lactose intolerance c. Virus infection d. Neither AIDS nor virus infection. e. All of these have been successfully treated using enzyme inhibitors.

Answer 70

b

Question 71

Which of the following is true about a mixed type inhibition? a. A Lineweaver-Burk plot will give parallel lines b. The KM will change but not the Vmax c. The lines of a Lineweaver-Burk graph will cross in the top left quadrant d. None of these is true

Answer 71

c

Question 72

Pure noncompetitive inhibition is a limiting case of a. Competitive inhibition b. Uncompetitive inhibition c. Irreversible inhibition d. Mixed inhibition e. None of these is true

Answer 72

d

Question 73

Which of the following is the most unique about an uncompetitive inhibitor? a. It affects the KM of the enzyme b. It affects the Vmax of the enzyme c. It can be identified by a Lineweaver-Burk plot d. The inhibitor can bind to ES but not to free E e. None of these is particularly unique to an uncompetitive inhibitor

Answer 73

d

Question 74

Which of the following is not related to the others? a. Suicide Substrate b. Irreversible Inhibitor c. Trojan Horse substrate d. Competitive Inhibitor e. All of these are related

Answer 74

d

Question 75

Nonenzymatic catalysts enhance the rate of a reaction by factors of _____. a. 10^5 to 10^9 b. 10^2 to 10^4 c. 10^15 to 10^20 d. 10^22 to 10^24

Answer 75

b

Question 76

Identify a true statement about the enzyme creatine kinase (CK). a. Creatine kinase (CK) is found only in brain and skeletal muscles. b. After a heart attack, creatine kinase (CK) shows up more rapidly in blood than lactate dehydrogenase (LDH). c. Creatine kinase (CK) is an isozyme as it can exist in five different forms. d. A high level of creatine kinase (CK) in brain indicates normal functioning of the brain.

Answer 76

b

Question 77

The rate of the reaction of glycogenn with inorganic phosphate, Pi , to form glucose-1-phosphate and glycogenn-1 is _____. a. rate = k[Glycogen]^1[Pi]^1 b. rate = k[Glycogen]^0[Pi]^1 c. rate = k[Glucose-1-phosphate]^1 [Pi]^1 d. rate = k[Glucose-1-phosphate]^0[Pi]^1

Answer 77

a

Question 78

The rate of a zero-order reaction depends on the _____. a. total number of reactants b. concentration of products c. concentration of reactants d. presence of catalysts

Answer 78

d

Question 79

Explain the mechanism of the lock-and-key model of enzyme-substrate binding

Answer 79

The lock-and-key model assumes a high degree of similarity between the shape of the substrate and the geometry of the binding site on the enzyme. The substrate binds to a site whose shape complements its own shape, like a key in a lock or the correct piece in a three-dimensional jigsaw puzzle.