Ch07 - The Behavior of Proteins: Enzymes, Mechanisms, and Control Flashcards
Which of the following best describes negative cooperativity?
a. Binding of one substrate molecule prevents the enzyme from working at all.
b. Binding of one substrate molecule inhibits the binding of a second substrate.
c. Binding of one substrate molecule enhances the binding of a second substrate.
d. Binding of one substrate molecule inhibits the binding of other effectors
b. Binding of one substrate molecule inhibits the binding of a second substrate.
The saturation curve for aspartyl transcarbamylase has a similar shape to the curve for:
a. Myoglobin
b. Hemoglobin
c. Chymotrypsin
d. Both hemoglobin and chymotrypsin.
e. All of these.
b. Hemoglobin
CTP is a known inhibitor of ATCase, the enzyme that catalyzes the first reaction in the pathway for the synthesis of this compound. This is an example of
a. irreversible inhibition
b. feedback inhibition
c. zymogenic inhibition
d. negative cooperativity
b. feedback inhibition
Homotrophic effects for allosteric enzymes involve
a. the same molecule binding to different sites in the enzyme.
b. different molecules binding to the same site in an enzyme.
c. different molecules binding to different sites in the same enzyme.
d. All of these are homotrophic effects.
a. the same molecule binding to different sites in the enzyme.
Enzyme kinetics falls into two general categories, simple saturation and cooperative kinetics.
a. True
b. False
a. True
M → N → O → P → Q → R
1 2 3 4 5
The final product, R, will most likely inhibit which reaction?
a. 1
b. 2
c. 3
d. 4
e. 5
a. 1
M → N → O → P → Q → R
1 2 3 4 5
Which two enzymes would be the most likely ones to regulate if this pathway is dedicated to the formation of only one product?
a. 1 and 2
b. 1 and 3
c. 1 and 5
d. 2 and 4
e. 4 and 5
a. 1 and 2
M → N → O → P → Q → R
1 2 3 4 5
Which two enzymes would be the most likely ones to regulate if this pathway is freely reversible and can go both ways?
a. 1 and 2
b. 1 and 3
c. 1 and 5
d. 2 and 4
e. 4 and 5
c. 1 and 5
Which of the following is a mechanism of regulating enzyme activity?
a. Feedback inhibition by product.
b. Addition or removal of phosphate groups from of the enzyme.
c. Presence of activators.
d. Activation of zymogens.
e. All of these regulate enzyme activity
e. All of these regulate enzyme activity
Which of the following is true?
a. Allosteric enzymes are rarely important in the regulation of metabolic pathways.
b. Michaelis-Menten kinetics describe the reactions of allosteric enzymes
c. Allosteric enzymes have a hyperbolic plot of reaction rate vs. substrate concentration
d. none of these is true
d. none of these is true
Which of the following is NOT required in order for an enzyme to display cooperative kinetics?
a. Multiple subunits.
b. A value for the Michaelis constant, KM.
c. Allosteric sites which affect the binding of substrate to the active site.
d. Ability to display a Vmax.
e. All of these are characteristic of cooperative enzymes.
b. A value for the Michaelis constant, KM.
In a comparison of allosteric and non-allosteric enzymes
a. it is always possible to define a KM
b. it is always possible to define a Vmax
c. competitive inhibition is always a possibility
d. much of the terminology is completely unchanged
b. it is always possible to define a Vmax
Is the Michaelis-Menten equation useful when studying allosteric enzymes?
a. Yes
b. No
c. Only if the enzyme displays positive cooperativity.
d. Only if the enzyme displays negative cooperativity.
b. No
Where do allosteric inhibitors bind on an enzyme?
a. They always bind at a site different from the active site.
b. They always bind at the active site.
c. They can bind at either active site or another site.
d. They always bind directly to the substrate
e. none of these
a. They always bind at a site different from the active site.
The term K0.5 is analogous to the KM
a. True
b. False
a. True
How do each of these compounds affect the function of ATCase?
a. ATP inhibits and CTP activates
b. ATP activates and CTP inhibits
c. Both ATP and CTP inhibit
d. Both ATP and CTP activate
b. ATP activates and CTP inhibits
How do each of these compounds affect the function of ATCase?
a. ATP is a K effector and CTP is a V effector.
b. ATP is a V effector and CTP is a K effector.
c. Both ATP and CTP are K effectors.
d. Both ATP and CTP are V effectors.
e. none of these
c. Both ATP and CTP are K effectors.
In reactions catalyzed by allosteric enzymes
a. substrate, activators, and inhibitors all compete for the same binding site on the enzyme.
b. there is no distinction between catalytic and regulatory subunits.
c. the presence of an activator makes the plot of reaction rate against substrate concentration less cooperative.
d. the presence of an inhibitor makes the plot of reaction rate against substrate concentration less cooperative.
c. the presence of an activator makes the plot of reaction rate against substrate concentration less cooperative.
A velocity curve (V vs. [S]) for a typical allosteric enzyme will be
a. a rectangular hyperbola.
b. a sigmoid curve.
c. a straight line.
d. a parabola.
e. none of these
b. a sigmoid curve.
ATP is a negative allosteric effector for glycogen phosporylase. This is an example of
a. feedback inhibition.
b. positive cooperativity.
c. negative cooperativity.
d. competitive inhibition.
a. feedback inhibition.
E1 E2 E3 E4
A → B → C → D → F (final product)
Which of the following would be an example of feedback inhibition?
a. the product of the final reaction, F, interacting with E1.
b. F interacting with an allosteric site in E4.
c. B interacting with an allosteric site in E1.
d. all of the intermediates or products in the reaction interacting with the active site in E1
a. the product of the final reaction, F, interacting with E1.
Allosteric enzymes must exhibit which of the following?
a. feedback inhibition
b. a phosphorylation site
c. general acid-base catalysis
d. a quaternary structure
e. none of these must be exhibited
d. a quaternary structure
What happens when a K-acting inhibitor is added to an allosteric enzyme system?
a. The apparent KM for the substrate increases.
b. The apparent KM for the substrate decreases.
c. The apparent Vmax for the substrate increases.
d. The apparent Vmax for the substrate decreases.
a. The apparent KM for the substrate increases.
The behavior of allosteric enzymes
a. does not play any role in feedback inhibition in metabolic pathways
b. is strongly dependent on the presence of metal ions
c. is related to their ability to hydrolyze themselves
d. depends on changes in their quaternary structure on binding of substrates or inhibitors
d. depends on changes in their quaternary structure on binding of substrates or inhibitors
The binding of aspartate to different subunits of ATCase is an example of
a. enzyme inhibition
b. a heterotropic effect
c. a homotropic effect
d. negative cooperativity
c. a homotropic effect
The concerted model for allosteric behavior was proposed by:
a. Koshland
b. Pauling
c. Pasteur
d. Monod, Wyman and Changeux
e. All of these
d. Monod, Wyman and Changeux
The sequential model for allosteric enzymes was proposed by:
a. Koshland
b. Pauling
c. Pasteur
d. Monod, Wyman and Changeux
e. All of these
a. Koshland
Which of the following does not apply to the concerted model for subunit behavior:
a. Each subunit can exist in a relaxed (R) and taut (T) conformation.
b. All subunits will be in either the R or the T conformation at the same time.
c. Some subunits can be in the R state while others are in the T state.
d. The presence of inhibitors will lead to more of the enzyme being in the T form
e. the presence of activators will lead to more of the enzyme being in the R form
c. Some subunits can be in the R state while others are in the T state.
In the concerted model for allosteric enzymes
a. the relative affinities of substrate for the T and R conformations plays an important role in the cooperativity of the reaction.
b. the equilibrium between the T and R conformations plays a minor role.
c. the enzymatic activity of the T conformation is considerably higher than that of the R form.
d. it is possible to describe the reactions of all allosteric enzymes accurately.
a. the relative affinities of substrate for the T and R conformations plays an important role in the cooperativity of the reaction.
In the concerted model, which state binds the substrate more tightly?
a. the relaxed (R) state
b. the taut (T) state
c. Both states bind equally well.
a. the relaxed (R) state
The sequential model for allosteric behavior
a. cannot account for reactions that display negative cooperativity.
b. postulates binding of substrates and inhibitors by the induced-fit model.
c. requires that the conformation of all subunits change simultaneously.
d. is mathematically simpler than the concerted model.
b. postulates binding of substrates and inhibitors by the induced-fit model.
In the concerted model the binding of the first substrate molecule will achieve all except
a. facilitation of the binding of other substrate molecules.
b. facilitation of the conversion of other subunits to the active state.
c. facilitation of the binding of inhibitors to the enzyme.
d. All of these are facilitated by the binding of the first substrate molecule.
e. None of these answers is correct.
c. facilitation of the binding of inhibitors to the enzyme.
In the concerted model the most active enzyme form will be when
a. all subunits are in the R state.
b. all subunits are in the T state.
c. there is a 50:50 mix of R & T states.
d. none of these
a. all subunits are in the R state.
According to the concerted model of allosteric behavior, an allosteric activator
a. favors the taut (tight) form of the enzyme.
b. favors the relaxed form of the enzyme.
c. can only bind to the enzyme if the substrate is already bound.
d. can only bind to the enzyme if the substrate has not already bound.
b. favors the relaxed form of the enzyme.