Chapter 7 Kinetics and Regulation
Matching Questions
Use the following to answer questions 1-10:
Choose the correct answer from the list below. Not all of the answers will be used.
a) first-order reaction
b) second-order reaction
c) metabolism
d) ensemble
e) biomolecular
f) turnover number
g) Michaelis
h) equilibrium
i) sequential
j) kinetics
k) initial reaction velocity
l) allosteric
m) ping-pong
1.
____________is a complex array of enzyme catalyzed reactions organized in multiple
pathways.
2.
_______________ is the study of rates of chemical reactions.
Ans:
Section: 7.1
3.
A reaction that is directly proportional to the concentration of reactant is a ____________.
Ans:
Section: 7.1
4.
A reaction with two substrates is considered a ____________ reaction.
Ans:
5.
At ____________ there will be no net change in the concentration of substrate or product.
Ans:
h
Section: 7.2
6.
The value Vo is called the ____________.
Ans:
k
Section: 7.2
Ans:
Section: Introduction
Chapter 7 Kinetics and Regulation
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7.
The kcat is often referred to as the ____________.
8.
The property that describes the enzyme-substrate interaction is measured by what constant?
Ans:
g
Section: 7.2
9.
____________ Enzymes that do not obey Michaelis–Menten kinetics.
Ans:
Section: 7.3
10.
____________ Experiments that determine the kinetics of a population of enzyme molecules.
Ans:
d
Section: 7.4
Fill–in-the-Blank Questions
11.
One way to measure the rate of an enzymatic reaction is to measure the loss of over time.
Ans: substrate Section: 7.1
12.
Reactions that have more than two reactants or substrates are considered reactions.
Ans: second-order Section: 7.1
13.
The rule states that all subunits in an allosteric enzyme must be in either the R or the R state;
no hybrids.
Ans: symmetry Section: 7.3
14.
The Michaelis–Menten model assumes that is the rate constant ignored because P has not
accumulated.
Ans: k–2 Section: Appendix
15.
is directly dependent on enzyme concentration.
Ans: Vmax Section: 7.2
16.
An enzyme will be most sensitive to changes in cellular substrate concentration when the
concentration is .
Ans: near the KM Section: 7.2
Ans:
Section: 7.2
Chapter 7 Kinetics and Regulation
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17.
The type of inhibition where the product of one enzyme inhibits another enzyme that acts
earlier in a metabolic pathway is considered a(an) inhibitor.
18.
Allosteric enzymes can be identified because the plot of initial velocity, V0, versus substrate
concentration, S, is not hyperbolic but -shaped.
Ans: sigmoidal Section: 7.3
19.
Negative allosteric stabilize the T-state of the enzyme.
Ans: effectors Section: 7.3
20.
The straight-line kinetic plot of 1/ V0 versus 1/S is called a .
Ans: Lineweaver–Burk plot, or double-reciprocal plot Section: 7.2
Multiple-Choice Questions
21.
A critical feature of the Michaelis–Menten model of enzyme catalysis is
A)
increasing the probability of product formation.
B)
shifting the reaction equilibrium.
C)
formation of an ES complex.
D)
All of the above.
E)
None of the above.
Ans: C Section: 7.2
22.
What value of [S], as a fraction of KM is required to obtain 20% Vmax? [S] =
A)
0.2 KM
B)
0.25 KM
C)
0.5 KM
D)
0.75 KM
E)
0.8 KM
Ans: B Section: 7.2
23.
Allosteric proteins:
A)
contain distinct regulatory sites and have multiple functional sites.
B)
display cooperativity.
C)
always consist of several identical subunits.
D)
A and B.
E)
A, B, and C.
Ans: D Section: 7.3
24.
Allosteric effectors alter the equilibria between:
A)
the ES state.
B)
the R and T forms of a protein.
C)
the forward and reverse reaction rate.
D)
the formation of product and it’s reverse reaction.
E)
All of the above.
Ans: feedback Section: 7.3
Chapter 7 Kinetics and Regulation
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25.
The formula V0 = Vmax [S] , indicates the relationship between
[S] + KM
A)
the enzyme activity and the equilibrium constant.
B)
the rate of a catalyzed reaction and the equilibrium constant.
C)
enzyme activity as a function of substrate concentration.
D)
All of the above.
E)
None of the above.
26.
The model describing allosteric regulation that requires all subunits to be in the same state is
called the ________.
A)
concerted model
B)
syncopated model
C)
cooperative model
D)
equilibrium model
E)
None of the above.
Ans: A Section: 7.3
27.
Loss of allosteric regulation in the production of purine nucleotides results in ___________.
A)
excess nucleotides for DNA
B)
loss of RNA due to ribose phosphate synthetase
C)
decreased urate degradation
D)
loss in urate concentration
E)
None of the above.
Ans: E Section: 7.3
28.
The KM is:
A)
equal to the product concentration at initial reaction conditions.
B)
equal to the substrate concentration when the reaction rate is half its maximal value.
C)
proportional to the standard free energy.
D)
All of the above.
E)
None of the above.
Ans: B Section: 7.2
29.
Given are five KM values for the binding of substrates to a particular enzyme. Which has the
strongest affinity when k−1 is greater than k2?
A) 150 mM B) 0.15 mM C) 150 M D) 1.5 nM E) 15,000 pM
Ans: D Section: 7.2
30.
When substrate concentration is much greater than KM, the rate of catalysis is almost equal to
A) Kd. B) kcat. C) Vmax. D) All of the above. E) None of the above.
Ans: C Section: 7.2
Ans: C Section: 7.2
Chapter 7 Kinetics and Regulation
5
31.
Which of the following is true under the following conditions: The enzyme concentration is 5
nM, the substrate concentration is 5 mM, and the KM is 5 M.
A)
The enzyme is saturated with substrate.
B)
Most of the enzyme does not have substrate bound.
C)
There is more enzyme than substrate.
D)
All of the above.
E)
None of the above.
32.
Homotrophic effects of allosteric enzymes:
A)
D)
shift the kinetics curve to the right.
B)
E)
None of the above.
C)
Ans: A Section: 7.3
33.
Multiple substrate enzyme reactions are divided into two classes:
A)
sequential reactions and double displacement reactions.
B)
double displacement reactions and concerted reactions.
C)
sequential reactions and concerted reactions.
D)
A and C.
E)
None of the above.
Ans: A Section: 7.2
34.
When [S] << KM, the enzymatic velocity depends on__________.
A)
the values of kcat/KM, [S], and [E]t
B)
the Vmax of the reaction
C)
the affinity of the substrate for the catalytic site
D)
kcat
E)
the formation of the ES complex
Ans: A Section: 7.2
35.
Allosteric effectors:
A)
can cause large changes in enzymatic activity.
B)
can lead to a decrease in the availability of a protein.
C)
do not alter the sensitivity of a metabolic pathway.
D)
decrease the sensitivity of the enzyme at nearly all concentrations of substrate.
E)
alter enzyme activity by binding to the active site of an enzyme.
Ans: A Section: 7.3
36.
For decades, enzymes have been studied using ensemble methods, but technology now allows
them to be studied in singulo. Which of the statements below states one of the significant
outcomes of this new technology?
A)
New methods better demonstrate cooperativity of allosteric enzymes.
B)
New methods allow for better determination of kcat.
C)
New methods reveal a distribution of enzyme characteristics.
D)
New methods validate the steady-state assumption of Michaelis–Menten kinetics.
E)
New methods provide understanding of average enzyme kinetic data.
Ans: A Section: 7.2
Chapter 7 Kinetics and Regulation
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37.
When reaction conditions are such that the amount of substrate is far greater than the amount of
enzyme present, then the following conditions are also met.
A)
The [substrate] is much less than KM.
B)
The V0 is half Vmax.
C)
The enzyme is displaying second-order kinetics.
D)
The enzyme is displaying first-order kinetics.
E)
The enzyme is displaying zero-order kinetics.
38.
During the early stages of an enzyme purification protocol, when cells have been lysed but
cytosolic components have not been separated, the reaction velocity versus substrate
concentration is sigmoidal. As you continue to purify the enzyme, the curve shifts to the right.
Explain your results.
A)
This is an enzyme that displays Michaelis–Menten kinetics, and you purify away a
homotrophic inhibitor.
B)
This is an enzyme that displays Michaelis–Menten kinetics, but you must use a
Lineweaver–Burk plot to determine KM and Vmax correctly.
C)
This is an allosteric enzyme, but you must use a Lineweaver–Burk plot to determine KM
and Vmax correctly.
D)
This is an allosteric enzyme, and during purification you purify away a heterotrophic
activator.
E)
This is an allosteric enzyme displaying a double-displacement mechanism, and during
purification you purify away one of the substrates.
Ans: D Sections: 7.2 and 7.3
39.
After purifying the enzyme in the previous question, you determine the Mr to be 75,000. By
assaying 5 μg of the enzyme under saturating [S] concentrations, you determine the Vmax to be
1.68 μmol/sec. Calculate the turnover number for this enzyme.
A)
2.25 106 sec-1
B)
1.50 105 sec-1
C)
2.50 104 sec-1
D)
1.79 105 sec-1
E)
You need to also know the KM for this enzyme to calculate turnover number.
Ans: D Section: 7.2
Short-Answer Questions
40.
In many enzyme assays, the natural substrate and product are not used. Why?
in products that can be easily measured. For example, substrates are chosen that result in
products that are colored and can be detected spectrophotometrically.
Section: 7.1
Ans: E Sections: 7.1 and 7.2
Chapter 7 Kinetics and Regulation
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41.
A protease hydrolyzes the peptide backbone. What is the substrate(s) and product for this
reaction? Assuming that the concentration of water is so high (~55M) that it does not
appreciably change, to what kind of reaction order would one assign this reaction?
42.
The rate of a reaction is dependent on [ES]. Using an enzyme catalyzed reaction scheme, (6),
describe the kinetic model for [ES].
resulting reaction where ES → EP → E + P (k2).
Section: 7.2
43.
Figure 7.8 is a simplified version of a common set of converging metabolic pathways. Describe
the type of regulation necessary if each of the reactions was reversed and a product, A or G,
were preferred.
Ans:
A feed-forward inhibition where a product, G or H, inhibits e1, e2, e3, or e5. Another
possibility is that one or more of the products A through F inhibits e10 or e11.
Section: 7.3
44.
Draw a Cleland notation for a sequential reaction and for a double-displacement reaction.
Ans:
See Figures 7.6 A and 7.6B.
Section: 7.2
45.
What is the Michaelis–Menten equation? Define all parameters.
Section: 7.2
46.
What does Vmax indicate?
Section: 7.2
zero and can be ignored, thus the rate of the reaction is directly proportionate to the
concentration of the protein and is a first-order reaction.
Section: 7.1
Chapter 7 Kinetics and Regulation
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47.
What is the upper limit of kcat / KM?
48.
How do the intermediate steps in multi-substrate enzyme mechanisms differ?
three is formed. In a double displacement (ping-pong), one or more products are released
prior to binding of all substrates. Thus, a substituted enzyme intermediate is formed.
Section: 7.2
49.
Describe the difference between the concerted and the sequential model of allosteric regulation.
conformation different from the neighboring subunits. In the former, substrate influences
have an intermediate impact on affinity and conformation.
Section: 7.3
50.
Would you expect the order of substrate binding to be critical for enzyme catalysis?
displacement, both conditions are observed. Substrates may need to bind in a particular
order (lactate dehydrogenase) or the enzyme may bind substrates and release products in
random order (creatine kinase).
Section: 7.2
51.
What is the turnover number for an enzyme and what does this value tell us about the enzyme?
which an enzyme saturated with substrate converts substrate to product. This is basically
the measure of the reaction without an impact on substrate binding and is dependent on
the concentration of enzyme and describes the relative speed of a reaction.
Section: 7.2
52.
When designing a drug to inhibit the formation of a product, which requires several enzymes in
a metabolic pathway, what should be the first piece of information a biochemist needs in order
to develop the drug?
Ans:
Find the committed step. In a metabolic pathway there will be a rate-limiting, committed
enzyme step that is often the target of physiological regulation. This protein would be the
best target for a new drug.
Section: 7.2
Ans:
The diffusion-controlled interaction of the substrate and enzyme determines the upper
limit of the rate. The upper limit is 108 – 109 s-1M-1.
Section: 7.2
Chapter 7 Kinetics and Regulation
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53.
How does the sequential model differ from the concerted model for allosteric enzymes?
54.
Draw a sketch of a Michaelis–Menten plot and a Lineweaver–Burk plot. Identify how you
would determine KM and Vmax from each of these plots. Explain why the Michaelis–Menten is
used more widely than the Lineweaver–Burk plot even though, in general, straight-line plots are
easier to interpret.
making them sensitive to errors. In addition, computer software has advanced to the point
computers than they were originally.
Section: 7.2
tense- or relaxed-form protein. In contrast, the sequential model allows for a mixed type
the ligand binding by a particular subunit.