Deck 12: Enzymes Kinetics and Specificity

Question 1

What is an enzyme's specificity a result of?

A)the ratio of catalyzed rate to the uncatalyzed rate of reaction
B)molecular recognition based on structural complementarity
C)amount of enzyme produced by the cell
D)amount of substrate available

Answer 1

B

Question 2

For an enzyme-catalyzed reaction,the initial velocity was determined at 2 different concentrations of the substrate.Which of the following would be closest to the value of Km?

A)0.17 Mm
B)0.60 mM
C)1.7 mM
D)2.7 mM

Answer 2

B

Question 3

How do enzymes work?

A)by providing an alternate reaction pathway
B)by increasing the spontaneity (DG)of the reaction
C)by lowering the activation energy of the reaction
D)by altering the concentration of the reactants to achieve a favourable DG

Answer 3

C

Question 4

What term describes an enzyme that is an ATP-dependent phosphotransferase?

A)isomerase
B)uricase
C)protease
D)kinase

Question 5

Where on the enzyme does the substrate bind in order for catalysis to occur?

A)at hydrophobic residues
B)at the active site
C)at the regulatory site
D)on the surface

Question 6

Which of the following is NOT correct for catalysts?

A)They work by lowering the energy of activation.
B)The average energy of the reaction is unchanged.
C)They combine transiently with the reactants,promoting a reactive transition state condition.
D)They are regenerated after each third reaction cycle.

Question 7

Which reaction would NOT proceed via bimolecular elementary steps?

A)C + D T + U
B)a reaction with a rate constant in the units of s-1
C)2A D + E
D)a reaction with a molecularity of 2

Question 8

Which of the following is NOT correct regarding the transition state of a reaction?

A)The transition state is located at the height of a free energy diagram.
B)The transition state,once reached,indicates that there is a high probability that the reaction will occur.
C)The energy required to raise the average energy of one mole of reactant to the transition state is the free energy of activation.
D)The transition state energy level is the sum of the energy levels of the reactants and products.

Question 9

Which of the following defines the kinetics of a reaction when every enzyme molecule in the reaction mixture has its substrate-binding site occupied by substrate?

A)The kinetics become zero order and the velocity is Vmax/2.
B)The kinetics become zero order and the velocity is Vmax.
C)The kinetics become first order and the velocity is Vmax/2.
D)The kinetics become first order and the velocity isVmax.

Question 10

What is the definition of the free energy of activation,DG‡?

A)the average free energy of the product formed
B)the rate of a chemical reaction in relationship to the concentration of reactant molecules
C)the energy required to raise the average energy of one mole of reactant to the transition state energy
D)the amount of energy released by a spontaneous reaction

Question 11

Which of the following is correct regarding the Michaelis-Menten constant,Km,for this kinetic mechanism?

A)Km is numerically equal to the substrate concentration required to achieve one half the maximum velocity.
B)Its defined as Km = k1/(k-1 + k2).
C)Km is approximately equal to the dissociation constant for the enzyme-substrate complex to E + P.
D)The numeric value of Km has the units of mole-1.

Question 12

Which of the following applies to the Briggs and Haldane steady-state assumption?

A)It is defined by the equation .
B)It states that the rate of enzyme-substrate complex formation differs from the rate of enzyme-substrate disappearance.
C)The concentration of the enzyme-substrate complex reaches a constant value,even in a dynamic system.
D)The enzyme-substrate complex will always dissociate to form E + P.

Question 13

If the rate constant for the enzyme-catalyzed reaction is 2 × 10⁵/sec,and the rate constant for the uncatalyzed reaction is 2 × 10-⁶/sec,what is the catalytic power of the enzyme?

A)2 × 10-11
B)10-1
C)2 × 10-1
D)1011

Question 14

Which of the following is NOT correct regarding the relationships between [S],Km,and Vmₐₓ?

A)As the [S] is increased,v approaches the limiting value,Vmax.
B)Km = Vmax/2.
C)The rate of the reaction,v,follows a first-order rate equation: v = K'[A] and K' = Vmax/Km.
D)The rate of product formed,v,is at Vmax when [S] >> Km.

Question 15

Which term defines the catalytically active complex of an apoenzyme and its prosthetic group?

A)catalytic duo
B)holoenzyme
C)prosthetic enzyme
D)dimeric enzyme

Question 16

How do catalysts work to accelerate a chemical reaction?

A)They raise the average energy of the reactants.
B)They raise the overall free energy change of the reaction
C)They lower the energy of activation.
D)They lower the overall free energy change of the reaction.

Question 17

Which of the following is NOT a property of coenzymes?

A)They are usually actively involved in the catalytic reaction of the enzyme.
B)They tend to be stable to heat.
C)They are protein components.
D)They can serve as intermediate carriers of functional groups.

Question 18

Which of the following is NOT a distinctive feature of enzymes?

A)regulatory
B)catalytic activity
C)ability to change DG
D)specificity

Question 19

If an enzyme has a Vmₐₓ of 15 mM/min,what is the velocity if the substrate is present at ¼ of the Km?

A)12 mM/min
B)6 mM/min
C)3.75 mM/min
D)3 mM/min

Question 20

Which of the following is NOT correct regarding enzyme pathways?

A)The most effective way to control the pathway is to regulate every enzyme in the pathway.
B)An enzyme pathway always proceeds in only one direction,never in reverse.
C)A regulatory enzyme is regulated only by molecules within the given pathway.
D)Metabolic pathways are necessary since enzymes usually catalyze only one specific reaction.

Question 21

Which of the following is NOT correct for a competitive inhibitor?

A)It binds a site other than the active site.
B)EI does not give rise to E + P.
C)For a given [I],v decreases.
D)At some point,S can displace all of I on E.

Question 22

Which of the following is NOT correct regarding competitive inhibition?

A)For a group-specific enzyme,one substrate would be a competitive inhibitor of reactions of the other possible substrate.
B)Sometimes a product of an enzyme-catalyzed reaction is a competitive inhibitor of its own production.
C)Competitive inhibitors usually interact with the enzyme at the binding site for a substrate.
D)In the presence of a competitive inhibitor,the apparent Km would be altered and V_max would be decreased.

Question 23

A plot of 1/V versus 1/[S] for an enzyme-catalyzed reaction gave a line with an equation of y = 0.5x + 0.2.The same enzyme with an inhibitor present gave a line with an equation of y = 1.1x + 0.2.Which of these statements is correct regarding the inhibition?

A)It is competitive.
B)It is non-competitive.
C)It is uncompetitive.
D)It is irreversible.

Question 24

What type of reaction is depicted in the following graph?

A)double-displacement bisubstrate reaction
B)competitively inhibited reaction
C)single-displacement bisubstrate reaction
D)mixed non-competitively inhibited reaction

Question 25

Which of the following is NOT a characteristic of ordered single-displacement reactions?

A)Lineweaver-Burk plots with lines that intersect to the left of the 1/v axis
B)a chemically modified enzyme intermediate
C)the lack of any exchange reaction activity
D)single substrate initial binding activity

Question 26

Which of the following is NOT correct for kcₐt?

A)referred to as the maximal velocity of the enzyme
B)called the turnover number of the enzyme
C)measures the maximal catalytic activity or kinetic efficiency of an enzyme
D)defines the number of substrate molecules converted into product/enzyme molecule/unit of time when the enzyme is saturated with substrate

Question 27

For an enzyme-catalyzed reaction,the initial velocity was determined at 2 different concentrations of the substrate.Which of the following would be closest to the value of Vmₐₓ?

A)0.32 mM/min
B)0.67 mM/min
C)1.5 mM/min
D)3.19 mM/min

Question 28

In the enzyme catalyzed reaction sequence below,can the E-PO₄- intermediate be predicted and why?

A)Yes,the mechanism is a double-displacement reaction.
B)Yes,the reaction fits the Ping-Pong model.
C)No,the reaction is random single displacement.
D)No,the reaction is double displacement.

Question 29

Which of the following is NOT a characteristic of kcₐt/Km?

A)It corresponds to a second-order rate constant.
B)It provides an excellent parameter for comparison of the catalytic efficiency of enzymes.
C)It reflects the property of the enzyme when substrate concentration is at saturation.
D)The upper limit for the kcat/Km value is fixed by the diffusion-controlled limit for reactions,which is 109 M⁻¹ s⁻¹.

Question 30

What type of enzyme inactivator is penicillin an example of?

A)competitive inhibitor
B)non-competitive inhibitor
C)suicide substrate
D)uncompetitive inhibitor

Question 31

Which of the following is a feature of uncompetitive inhibition?

A)I combines only with ES.
B)I combines only with E.
C)I combines with E and ES.
D)I combines with EP.

Question 32

Which molecules does Sildenafil citrate (Viagra)inhibit?

A)acid phosphatases
B)cAMP phosphodiesterases
C)glycogen phosphorylase
D)cGMP phosphodiesterases

Question 33

In the reaction mechanism below,which components are competitive for binding to free enzyme E?

A)P and A
B)A and B
C)B and Q
D)Q and A

Question 34

Which of these antibiotics acts by forming a covalent derivative of the enzyme glycoprotein peptidase?

A)antimycin
B)neomycin
C)oligomycin
D)penicillin

Question 35

Which of these statements describes the pH optimum of an enzyme?

A)always between pH 6 and pH 8
B)nearly the same for all enzymes
C)pretty broad over 6 to 8 pH units
D)occurs when there is optimum secondary and tertiary structure in the active site of the enzyme

Question 36

In transforming the Michaelis-Menten equation into a straight-line equation,y = mx + b,the Lineweaver-Burk double reciprocal plot is generated.Which of the following is NOT a correct representation of this plot?

A)y-intercept is 1/Vmax
B)y = 1/V
C)x-intercept is 1/Km
D)x = 1/[S]

Question 37

Which of the following will glutamate react with to form a-ketoglutarate in the glutamate:aspartate aminotransferase-catalyzed reaction mechanism?

A)E-pyridoxal phosphate complex
B)E-pyridoxamine phosphate complex
C)aspartate
D)oxaloacetate

Question 38

Which of the following is NOT correct regarding non-competitive inhibition?

A)Non-competitive inhibitors interact with the enzyme as well as the enzyme-substrate complex.
B)Increasing the concentration of [S] can overcome the inhibition.
C)The V_max value does not remain the same as for a reaction that is not inhibited.
D)The inhibitor can cause a conformational change in the enzyme.

Question 39

What is malonate inhibition of succinate dehydrogenase an example of?

A)non-competitive inhibition
B)competitive inhibition
C)irreversible inhibition
D)uncompetitive inhibition

Question 40

What is the basis for the International Units of an enzyme?

A)ratio of enzyme to other proteins
B)micromoles of product formed per minute
C)moles of substrate reacted
D)micromoles of product produced at Vmax/2

Question 41

Against which type of antigen is a catalytic antibody (abzyme)generated?

A)an analog of the transition-state intermediate in the reaction
B)the substrate of the reaction
C)an analog of the product of the reaction
D)an analog of the transition-state intermediate in the reaction

Question 42

Which of the following is NOT a characteristic of ribozymes?

A)They emerge from the reaction changed.
B)They are substrate specific.
C)They enhance the reaction rate.
D)They are RNA molecules.

Question 43

Which of the following is NOT a characteristic of the enzyme hexokinase?

A)It is highly specific and will only catalyze phosphorylation of glucose and fructose.
B)Hexoses bind the active site and induce a solvent-inaccessible fit to the hexose.
C)Glycerol may fit into the active site,but it does not bind to induce a conformational change necessary for catalysis.
D)When a hexose binds the active site,the active site is modified to promote changes in the substrate to a transitional-state intermediate.