The Behavior of Proteins: Enzymes Flashcards
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.
e
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
c
The rate of a reaction depends on
a. the free energy change
b. the activation energy
c. the enthalpy change
d. the entropy change
b
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
d
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.
a
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
d
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.
c
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.
d
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.
c
The rate of a reaction is always dependent on the concentration(s) of the reactant(s).
a. True
b. False
b
All catalysts work by lowering the activation energy for a reaction.
a. True
b. False
a
The amount of energy released during a reaction tells nothing about the rate at which that reaction will occur.
a. True
b. False
a
Thermodynamically favorable reactions all release energy.
a. True
b. False
a
The sign of Gibb’s Free Energy is positive (“+”) when energy is released.
a. True
b. False
b
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
e
The order of a reaction can be determined from the balanced equation for the reaction.
a. True
b. False
b
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
b
Given the rate law, rate = k[A][B], the overall reaction order is
a. zero
b. one
c. two
d. cannot be determined
c
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.
b
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
d
The substrate will only bind to the enzyme when the shapes fit together rigidly.
a. True
b. False
b
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
c
The E-S complex often shows as a slight depression in the energy profile for the reaction.
a. True
b. False
a
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
d
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
e
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
d
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
e
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.
c
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
d
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
a
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.
b
