BCH400/600
Name___________________
Exam 2
March 4, 2002
For questions 1 through 30mark the correct answer on the scantron answer sheet and this
exam
Multiple-choice questions (2 points per question)
1) Allosteric enzymes _____________.
(a) usually have quaternary structure.
(b) do not behave according to Michaelis-Menton kinetics.
(c) bind allosteric modulators at sites not associated with substrate binding.
(d) often have separate catalytic and regulator domains.
(e) all of the above.
2) A catalyst can promote product formation during a chemical reaction by _____.
(a) lowering the activation energy barrier.
(b) stabilizing the transition state.
(c) positioning reactants in the correct orientation.
(d) bringing reactants together.
(e) all of the above
3) The rate of sucrose hydrolysis (sucrose + H20 <-> fructose + glucose) is dependent
on the concentration of sucrose and independent of the concentration of H20.
Therefore this reaction is a ______.
(a) 1st order reaction in relation to water.
(b) zero order reaction in relation to sucrose.
(c) 1st order reaction in relation to sucrose
(d) 2nd order reaction in relation to sucrose and water.
(e) none of the above.
4) The initial velocity assumption for Michaelis-Menton kinetic assumes that
______.
(a) The reaction is always running at Vmax.
(b) the rate of E + P -> ES is negligible.
(c) a large amount of product has formed.
(d) k-2 is large.
(e) none of the above.
5) Km is _______.
(a) the substrate concentration at ½ Vmax.
(b) = (k-1 + kcat)/k1
(c) related to an enzymes affinity for a specific substrate.
(d) the Michaelis Constant.
(e) All of the above
(f)
6) Heterolytic carbon-carbon bond cleavage can result in the formation of_____.
(a) a carbocation.
(b) radical species.
(c) a carbanion.
(d) a and b
(e) a and c
7) A reversible inhibitor that only binds to the ES complex is referred to as a _____.
(a) competitive inhibitor.
(b) non-competitive inhibitor.
(c) uncompetitive inhibitor.
(d) suicide inhibitor.
(e) irreversible inhibitor.
8) Chymotrypsin is an example of a
(a) transferase.
(b) hydrolase.
(c) oxidoreductase.
(d) lyase.
(e) isomerase.
9) NADH would function as a cofactor for a
(a) transferase.
(b) hydrolase.
(c) oxidoreductase.
(d) ligase.
(e) isomerase.
10) Lipoamide is ____________.
(a) a co-substrate.
(b) a metabolite coenzyme.
(c) a vitamin
(d) a prosthetic group.
(e) none of the above.
11) ______________ is a cosubstrate.
(a) Tetrahydrofolate.
(b) NADH
(c) Biotin
(d) Thiamin pyrophosphate.
(e) Pyridoxol phosphate
12) _________ is the coenzyme involved in decarboxylation reactions.
(a) Tetrahydrofolate.
(b) NADH
(c) Biotin
(d) Thiamin pyrophosphate.
(e) Pyridoxol phosphate.
13) The apparent Km of an enzyme changes when the enzyme is treated with a_____.
(a) competitive inhibitor.
(b) uncompetitive inhibitor.
(c) noncompetitive inhibitor
(d) a and b.
(e) b and c.
14) When glucose cyclizes, _________.
(a) it becomes a hemiketal.
(b) it looses one chiral center.
(c) the hydroxyl group associated with the anomeric carbon is always in the
beta conformation
(d) it usually forms a pyranose ring.
(e) none of the above
15) The amino acid ________ can function in proton transfer when present in the
enzyme active site.
(a) glutamate
(b) aspartate
(c) histidine
(d) lysine
(e) all of the above
16) Which of the following coenzymes participates in enzymatic mechanisms by
producing a free radical intermediate?
(a) NADPH
(b) Ubiquinone
(c) Methylcobalamin
(d) Biotin
(e) Lipoamide
17) Monosaccharides that differ at only one chiral center are referred to as _____.
(a) isosaccharides.
(b) enantiomers.
(c) epimers.
(d) anomers.
(e) none of the above.
18) N-linked oligosaccharides ____________.
(a) are involved in targeting proteins to different subcellular organelles
(b) are linked to amino acids with hydroxyl groups.
(c) are not required for correct protein folding of N-linked glycosylated
proteins.
(d) have no affect on the physical properties of a protein.
(e) All of the above
True or false (2 points per question
19) Under physiological conditions, the substrate concentration is < to the Km.
(a) true
(b) false
20) The enzyme active site binds the substrate with higher affinity than the transition
state.
(a) true
(b) false
21) Starch and glycogen are polysaccharides formed from alpha-1,4 and alpha-1,6
linked glucose molecules.
(a) true
(b) false
22) Starch forms a helical structure that can bind iodine to form a blue colored
compound.
(a) true
(b) false
23) Biotin forms a Schiff base in reactions with amine groups.
(a) true
(b) false
24) All monosaccharides are reducing sugars.
(a) true
(b) false
25) Lineweaver-Burk plots describe the equation of a rectangular hyperbolic curve.
(a) true
(b) false
26) The coenzyme FADH always transfers two electrons in the form of a hydride ion
during oxidation-reduction reactions.
(a) true
(b) false
27) The coenzyme FADH can form a semiquinone intermediate and therefore can
transfer electrons either one or two at a time.
(a) true
(b) false
28) An uncompetitive inhibitor decreases both the Km and the Vmax of a biochemical
reaction.
(a) true
(b) false
29) Pyranose monosaccharides are most stable when in the boat conformation
(a) true
(b) false
30) Metal activated enzymes bind to metal ions tightly as prosthetic groups within
the active site.
(a) true
(b) false
31) (10 points) Draw the Fischer and Haworth projections for beta-D-galactose.
Circle the anomeric carbon. Make sure to include all hydrogens and hydroxyl
groups. Determine the number of possible stereoisomers for both the open chain
and cyclized forms.
32) (10 points) Label the coenzyme with the correct name. Circle the active group(s)
on the chemical structure. For extra credit (one point per compound) double
circle the portion of the structure coming from the vitamin precursor.
H
C
O
O
P
O
O
O
H2C
O
N
H
O
H
C
NH2
N
O
H2
C
O
PO2-
OH OH
NH2
O
N
PO2-
N
O
CH2
O
N
OH OPO3-
N
CH3
33) (20 points) The kinetic data from an enzyme catalyzed reaction performed with
and without inhibitor is given below. From this information determine the Km’s
and Vmax’s for the enzyme with and without inhibitor by plotting the data on a
Lineweaver Burk (double reciprocal) plot. Label X-axis and Y-axis with correct
title and units. Determine the type of inhibition that is occurring in this
experiment.
[S] (μmoles/L)
Vo (μmoles/minute)
Vo (μmoles/minute)
without inhibitor
with inhibitor
1.5
0.21
0.11
2.0
0.24
0.12
3.0
0.28
0.14
4.0
0.33
0.16
8.0
0.40
0.20
16.0
0.45
0.23
Use the graph paper provided and show your work for partial credit.
12
11
10
9
8
7
6
Y Axis
5
4
3
2
1
0
-1
-2
-3
-4
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0
0.1
X Axis
0.2
0.3
0.4
0.5
0.6
0.7
29) (10 points) Vmax = Kcat [total enzyme]. Using the Vmax determined in question 27
and given that the total enzyme concentration used in the experiments above is 5.0 X
10-3 μM calculate Kcat. Make sure to designate the correct units. How much time does
it take for a single reaction to occur? If an alternative substrate had a Kcat/Km value of
150 μM-1 minutes –1, which substrate is most preferred by the enzyme, the original
substrate or the alternative substrate? Explain. (show work for partial credit).
BCH400/600
Exam 2
March 3, 2003
Name___________________
Multiple-choice questions. Circle the single correct answer. (2 points per question)
34) Enzyme cofactors that bind covalently at the active site of an enzyme are referred
to as _________.
(a) cosubstrates.
(b) prosthetic groups.
(c) apoenzymes.
(d) vitamins
35) Which of the following kinetic parameters best describes how well suited a
specific compound functions as a substrate for a particular enzyme?
(a) Km
(b) Vmax
(c) kcat
(d) kcat/Km
36) Which of the following is characteristic of an enzyme catalyst?
(a) It positions reactants in the correct orientation.
(b) It lowers the activation energy barrier.
(c) It binds the transition state tighter than the substrate.
(d) all of the above
37) The term ligase refers to a class of enzymes that catalyzes_________.
(a) oxidation reduction reactions.
(b) reactions involving the transfer of a functional group from one molecule to
another.
(c) hydrolytic cleavages.
(d) reactions where two molecules are joined together.
38) The rate of a second order reaction depends on the concentration of _________.
(a) one substrate
(b) two substrates
(c) three substrates
(d) none of the above
39) The steady state assumption for Michaelis-Menton kinetics assumes that ______.
(a) the concentration of the ES complex is constant.
(b) the rate of ES formation is faster than the rate of ES disassociation.
(c) k1 = k-1= kcat
(d) none of the above.
40) An enzyme is said to be catalytically perfect when _______.
(a) it has a large Km
(b) it has a small kcat
(c) its kcat/Km value is close to that of the diffusion limit
(d) it has very high affinity for the transition state.
41) Homolytic carbon-carbon bond cleavage can result in the formation of_____.
(a) a carbocation.
(b) radical species.
(c) a carbanion.
(d) a and b
(e) a and c
42) A reversible inhibitor that can bind to either E alone or the ES complex is referred
to as a _____.
(a) competitive inhibitor.
(b) non-competitive inhibitor.
(c) uncompetitive inhibitor.
(d) suicide inhibitor.
(e) irreversible inhibitor.
43) Cysteine and serine residues can function in ___________ when present in the
active site of an enzyme.
(a) anion binding
(b) cation binding
(c) proton transfer
(d) acyl group binding
44) Nicotinamide is ____________.
(a) a co-substrate.
(b) a metabolite coenzyme.
(c) a vitamin
(d) a prosthetic group.
(e) none of the above.
45) Which of the following is true for a covalent catalysis based enzymatic
mechanism.
(a) A covalently modified enzyme intermediate is involved.
(b) The enzyme undergoes a sequential reaction.
(c) The enzyme undergoes a ping pong reaction.
(d) a and b
(e) a and c
46) When the rate of an enzymatic reaction is controlled by the amount of enzyme
present, which of the following factors controls enzyme levels?
(a) rates of transcription
(b) rates of translation
(c) rates of protein turnover
(d) rates of mRNA turnover
(e) all of the above
47) The Vmax of an enzyme changes when the enzyme is treated with a_____.
(a) competitive inhibitor.
(b) uncompetitive inhibitor.
(c) noncompetitive inhibitor
(d) a and b.
(e) b and c.
48) The beta-1,4-glycosidic linkages of chitin and cellulose give these
polysaccharides which of the characteristics?
(a) Straight chain linear conformations.
(b) Helical conformations.
(c) Digestibility by humans.
(d) none of the above
49) Which of the following coenzymes forms a Schiff’s base during catalysis?
(a) NADH
(b) thiamin pyrophosphate
(c) lipoamide
(d) pyridoxal phosphate
(e) coenzyme A
50) Which of the following coenzymes functions in acyl transfer reactions?
(a) NADPH
(b) Coenzyme A
(c) biotin
(d) a and b
(e) b and c
51) Monosaccharides that differ at more than one chiral center and are not mirror
images of each other are referred to as _____.
(a) diasteromers
(b) enantiomers.
(c) epimers.
(d) anomers.
52) O-linked oligosaccharides ____________.
(a) are present in proteins that adopt extended conformations
(b) are linked to amino acids with hydroxyl groups.
(c) have no affect on the physical properties of a protein.
(d) a and b
(e) b and c
53) Which coenzyme can only accept/donate electrons 2 at a time?
(a) FAD+/FADH
(b) NAD+/NADH
(c) Lipoamide
(d) Coenzyme A
(e) None of the above
54) Which coenzyme is covalently bound to the enzyme active site?
(a) NAD+/NADH
(b) Lipoamide
(c) Coenzyme A
(d) None of the above
55) Pyranose sugars are most stabile in the ________ conformation?
(a) chair
(b) boat
(c) twist
(d) envelope
56) The most reduced carbon in a cyclized sugar is always referred to as
___________.
(a) the epimeric carbon
(b) the anomeric carbon
(c) the alpha carbon
(d) none of the above
57) Which polysaccharide is the most highly branched?
(a) Cellulose
(b) Chitin
(c) Glycogen
(d) Starch
58) Which of the following compounds is a metabolite coenzyme?
(a) NAD+/NADH
(b) Coenzyme A
(c) ATP
(d) Retinal
59) The catalytic triad present in serine proteases contain which three amino acids?
(a) Glu, Cys, Ser
(b) Asp, His, Ser
(c) Ser, Ala, Tyr
(d) Arg, His, Ser
60) Enzymes that are activated by proteolytic cleavage are referred to as __________.
(a) covalently modified enzymes
(b) enzyme complexes
(c) zymogens
(d) polymerized
61) Which of the following is true of enzymes that are regulated by allosteric
regulation?
(a) They are usually multimeric enzymes.
(b) A hyperobolic curve results from the plotting of Vo vs [S].
(c) They behave according to Michaelis-Menton kinetics.
(d) a and b
(e) b and c
62) N linked glycosylation of a protein can _____________.
(a) determine the subcellular locale of a protein
(b) determine the native structure of a protein
(c) protect a protein from proteolysis
(d) a and b
(e) all of the above
63) Which of the following is true in regards to kcat?
(a) kcat can be determined only if the concentration of enzyme [E] is known.
(b) kcat is referred to as the turnover number.
(c) According to Michaelis-Menton kinetics, kcat determines the rate of ES
complex formation
(d) a and b
(e) a and c
SHORT ANSWER QUESTIONS
64) (10 points total)
(a) (6 points) Draw the Fischer and Haworth projections for beta-D-fructose.
Make sure to include all hydrogens and hydroxyl groups.
(b) (2 points) Circle the anomeric carbon.
(c) (2 points) Determine the number of possible stereoisomers for both the
open chain and cyclized forms.
65) (10 points total)
(a) (1.25 points each) Label the coenzyme with the correct name.
(b) (1.25 points each) Circle the active group(s) on the chemical structure.
R = CH3
66) (10 points) The kinetic data from an enzyme catalyzed reaction is given below.
(a) (5 points) Using the data in the table below, graph the correct Lineweaver
Burk (double reciprocal) plot using the graph paper provided. Label the x
and y axis with the correct units.
(b) (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax
of the enzyme. Show your work for partial credit.
[S] (μmoles/L)
Vo (μmoles/minute)
0.1
0.2
0.5
0.8
1.0
2.0
3.33
5.00
7.14
8.00
8.33
9.09
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
-6 -4 -2
0
2
4
6
8
10
67) (10 points total)
(a) (2.5 points)On the same graph above in question 33, draw a DASHED line
depicting what the plot would look like if a noncompetitive inhibitor was
added to the reaction.
(b) (5.0 points) Describe what happens to the Km and Vmax values when a
noncompetitive inhibitor is added to the reaction.
(c) (2.5 points) What form of the enzyme does a noncompetitive inhibitor
bind?
EXTRA CREDIT (5 points): The rate of an enzymatic reaction is measured with three
similar but different substrates. From the experiments, the Km and kcat values were
determined for each substrate.
Km (mM)
kcat (s-1)
Compound A
31
0.06
Compound B
15
0.14
Compound C
25
2.80
Based on this data, answer the following questions:
(a) Which compound binds tightest to the enzyme? Explain your answer.
(b) Which compound is the best substrate for the enzyme? Explain your answer.
BCH400/600
Exam 2
March 1, 2004
Name___________________
Multiple-choice questions. Circle the single correct answer. (2 points per question)
68) An enzyme without its required co-factor prosthetic group is referred to as the
____________________.
i. coenzyme
ii. apoenzyme
iii. holoenzyme
iv. none of the above
69) An enzyme that catalyzes the addition of a chemical group to a double bond is
referred to as a ________________________.
i. oxidoreductase
ii. isomerase
iii. lyase
iv. transferase
70) What is the enzyme classification for the enzyme that catalyzes the following
reaction?
Pyrophosphate + H20 Æ 2 Phosphates
i. oxidoreductase
ii. hydrolase
iii. lyase
iv. ligase
71) Which of the following is a property of a catalyst?
i. It alters the equilibrium of the catalyzed reaction.
ii. It binds substrates.
iii. It is altered during the course of the reaction.
iv. It increases the activation energy barrier.
72) A pseudo-first order reaction____________________.
i. is a two substrate reaction whose rate depends on the
concentration of both substrates
ii. is a single substrate reaction whose rate depends on the
concentration of that substrate
iii. is two substrate reaction whose rate depends on the concentration
of only one of the substrate
iv. is two substrate reaction whose rate is independent of either
substrate
73) ____________________ is the term that describes a theoretical value achieved
when all enzyme substrate binding sites are occupied by the substrate.
i. Km
kcat
ii.
iii. Vmax
iv. kcat/ Km
74) The initial velocity assumption of the Michaelis-Menton equation states that
__________.
i. the rate of ES formation is equal to the rate of ES turnover
ii. a large amount of product is formed
iii. the rate of the P Æ ES reaction is negligible
iv. a and b
v.
b and c
75) Which of the following is best used to determine how well a specific substrate is
used by a specific enzyme?
i. Km
kcat
ii.
iii. Vmax
iv. kcat/ Km
76) If the absolute concentration of enzyme is unknown, which of the following
values can not be determined experimentally?
i. Km
kcat
ii.
iii. Vmax
iv. None of the above
77) Below is a list of five substrates and their corresponding Km values for enzyme X.
Based on this information which of the substrates binds tightest to the enzyme?
i. substrate A (Km = 2.1 X 10-6)
ii. substrate B (Km = 5.4 X 10-4)
iii. substrate C (Km = 7.0 X 10-6)
iv. substrate D (Km = 1.5 X 10-5)
78) Which type of multisubstrate reaction involves an intermediate step where the
enzyme is covalently modified by one of the substrates?
i. Sequential ordered reactions
ii. Sequential random reactions
iii. Ping-pong reactions
iv. a and b
v.
none of the above
79) Which of the following can be determined from a Lineweaver-Burk plot?
i. Km
kcat
ii.
iii. Vmax
iv. a and c
v.
all of the above
80) A competitive inhibitor binds to _____________its corresponding enzyme.
i. substrate binding site
ii. a site distal to the substrate binding site
81) Which of the following reversible inhibitors alter an enzyme’s function by
increasing the Vmax of the enzyme?
i. competitive inhibitor
ii. non-competitive inhibitor
iii. uncompetitive inhibitor
iv. none of the above
82) Covalent modifications that increase the activity of allosterically regulated
enzymes do so by ______________.
i. adding phosphate groups to essential amino acids in the active
site
ii. causing the enzyme to fold into a more active configuration
iii. increasing the amount of total enzyme present
iv. none of the above
83) Enzymes that are allosterically regulated _____________________.
i. are multimeric proteins
ii. possess regulatory and catalytic domains
iii. do not behave according to the Michaelis-Menton equation
iv. all of the above
84) ______________ are highly unstable and short living chemical species.
i. substrates
ii. products
iii. transition state intermediates
iv. intermediates
85) Conserved serine, histidine and aspartate residues are present in the catalytic
center of all serine proteases. Which of the following describes the role of the
histidine residue in the mechanism of this reaction?
i. covalent binding of acyl groups
ii. hydrophobic stabilization of the substrate
iii. proton transfer
iv. cation binding
86) _____________ form helical polysaccharides.
i. glycogen
ii. amylose
iii. chitin
iv. cellulose
v.
a and b
vi. c and d
87) What types of interaction allow multiple strands of cellulose to interact to form
cable like structures?
i. hydrophobic interactions
ii. covalent bonds
iii. hydrogen bonds
iv. ionic interactions
88) Which of the following can form the largest number of steroisomers?
i. An 6 carbon sugar in the hemiacetal form
ii. An 6 carbon sugar in the aldose form
iii. An 6 carbon sugar in the hemiketal form
iv. An 6 carbon sugar in the ketose form
89) Which type of glycoslyation is found in proteins whose function requires an
elongated conformation?
i. N-linked glycosylation
ii. O-linked glycosylation
iii. None of the above
90) Enzymes that cleave glycosidic linkages belong to which class of enzyme?
i. oxidoreductases
ii. lyases
iii. hydrolases
iv. transferases
91) Which cofactor has the following properties: a) forms Schiff base, b) its precursor
is absorb dietarily as Vitamin B6, c) is required in a number of reactions in amino
acid metabolism.
i. thiamin pyrophosphate
ii. biotin
iii. lipoamide
iv.
pyridoxal phosphate
92) Mg 2+ is used as a(n) _________ by metal activate enzymes that utilize negatively
charged substrates like ATP.
i. metalloenzyme
ii. activator ion
iii. prosthetic group
iv. co-substrate
Short Answer Questions
93) (10 points total)
(a) (6 points) Draw the Fischer and Haworth projections for alpha-D-glucose.
Make sure to include all hydrogens and hydroxyl groups.
(b) (2 points) Circle the anomeric carbon.
(c) (2 points) Determine the number of possible stereoisomers for both the
open chain and cyclized forms.
94) (10 points total)
(a) (1.25 points each) Label the coenzyme with the correct name.
(b) (1.25 points each) Circle the active group(s) on the chemical structure.
H
O
C
NH2
N
O
H2
C
O
PO2-
OH OH
NH2
O
N
PO2-
N
O
CH2
O
N
N
OH OPO3-
O
HC
O
O
P
O
O
H2C
O
N
H
CH3
95) (10 points) The kinetic data from an enzyme catalyzed reaction is given below.
(a) (5 points) Using the data in the table below, graph the correct Lineweaver
Burk (double reciprocal) plot using the graph paper provided.
(b) (5 points) Label the x and y axis with the correct units.
(c) (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax
of the enzyme. Show your work for partial credit.
[S]
(μmoles/L)
0.2
0.4
0.8
1
2
4
1/[S]
Vo
(μmoles/minute)
5
7.69
10
10.6
12.5
13.5
5
2.5
1.25
1.0
0.5
0.25
1/Vo
0.2
0.13
0.10
0.094
0.080
0.074
0.2
0
0.18
0.16
0.14
0
0.12
0.1
0
0
0.08
0
0.06
0.04
0.02
0
-5
-4
-3
-2
-1
0
1
2
3
4
5
96) (10 points total)
(a) (2.5 points)On the same graph above in question 33, draw a DASHED line
depicting what the plot would look like if an uncompetitive inhibitor was
added to the reaction.
(b) (5.0 points) Describe what happens to the Km and Vmax values when a
uncompetitive inhibitor is added to the reaction.
(c) (2.5 points) What form of the enzyme does an uncompetitive inhibitor
bind?
97) (5 points) Describe what would happen if an enzyme bound to the substrate
tighter than it binds to the transition state intermediate. Is this a catalytically
favorable situation?
EXTRA CREDIT (5 points): What are the four limitation of Michaelis Menton kinetics?
ANSWER ON BACK PAGE
BCH400/600
Exam 2
March 1, 2005
Name___________________
Multiple-choice questions (2 points per question)(enter the correct letter for each
answer on your scantron answer sheet)
98) Which of the following are properties of a cosubstrate?
(a) They are covalently attached to the active site of the enzyme.
(b) Once they have been involved in an enzymatic reaction require a separate
unrelated enzymatic reaction to be converted to their original state.
(c) They remain unchanged over the course of a reaction.
(d) b and c
(e) all of the above.
99) A catalyst can promote product formation during a chemical reaction by _____.
(a) lowering the activation energy barrier.
(b) stabilizing the transition state.
(c) positioning reactants in the correct orientation.
(d) bringing reactants together.
(e) all of the above
100)
The rate of sucrose hydrolysis (sucrose + H20 <-> fructose + glucose) is
dependent on the concentration of sucrose and independent of the concentration
of H20. Therefore this reaction is a ______ order reaction in respect to water.
(a) zero
(b) 1st
(c) 2nd
(d) 3rd
(e) none of the above.
101)
The assumption that the rate that E + P Æ ES is negligible is related to the
_________ Assumption of the Michaelis- Menton Model of Enzyme Kinetics.
(a) Steady State
(b) Equilibrium
(c) Initial Velocity
(d) none of the above.
102)
(k-1 + kcat)/k1 = _________.
Vmax
(b) Km
(c) Kcat
(d) Kcat/Km
(e) All of the above
(a)
103)
(a)
(b)
(c)
(d)
(e)
The formation of a carbocation results from a _______ cleavage reaction.
homolytic
heterolytic
radical
a and b
none of the above
104)
(a)
(b)
(c)
(d)
(e)
An uncompetitive inhibitor binds to _____.
E
ES
P
a and b
a and c
(a)
(b)
(c)
(d)
A holoenzyme refers to the form of the enzyme__________________.
that has the cofactor attached
that does not have the cofactor attached
that is normally inactive
none of the above
105)
106)
Which of the following can be calculated from a Lineweaver-Burk plot?
(a) Km
(b) Kcat
(c) Vmax
(d) b and c
(e) a and c
107)
Which of the following best describes the ability of an enzyme to convert
the ES complex to E + P?
(a)Vmax
(b) Km
(c) Kcat
(d) Kcat/Km
(e) All of the above
108)
When fructose cyclizes, _________.
(a) it looses one chiral center
(b) the hydroxyl group associated with the anomeric carbon is always in the
beta conformation
(c) it always forms a pyranose ring.
(d) none of the above
109)
The amino acid ________ can function in proton transfer when present in
the enzyme active site.
(a) glutamate
(b) aspartate
(c) histidine
(d) lysine
(e) all of the above
110)
(a)
(b)
(c)
(d)
(e)
Glycosidic linkages are formed through _________reactions.
hydrolytic
proteolytic
condensation
oxidation
reduction
B.
A.
H
C
O
D. H
O
O
O
C
NH2
P
O
O
H2C
O
N
N
H
O
H2
C
O
PO2-
C.
OH OH
NH2
O
N
PO2-
N
O
CH2
O
N
N
OH OPO3-
Questions 14 thru 20 (2 points each) Match the correct letter from the figure above to
correct description below. Enter “E” for none of the above. Make sure to enter the correct
letter on your scantron answer sheet.
111)
______ Functional group on Coenzyme A
112)
______ Functional group on thiamin-pyrophosphate
113)
______ Functional group on nicotinamide adenosine dinucleotide
phosphate.
114)
______ Functional group on pyridoxol phosphate
115)
______ Functional group involved in acyl group transfer
116)
______ Functional group that can accept 2 electrons as an hydride ions
CH3
117)
______ Functional group that can form a Schiff’s base with an amino
group
Multiple-choice questions (2 points per question)(enter the correct letter for each
answer on your scantron answer sheet)
118)
A(n) ______ does not bind to the active site of an enzyme.
a) substrate
b) competitive inhibitor
c) allosteric effector
d) a and b
e) all of the above
119)
Multi-substrate enzymes that use covalent catalysis mechanisms follow
_______.
a) order sequential kinetics
b) random sequential kinetics
c) Ping-Pong kinetics
d) None of the above
120)
The activity of a zymogen is activated by____________.
a) covalent modifications
b) allosteric regulation
c) association/disassociation of subunits
d) proteolytic modification
e) none of the above
121)
Allosteric enzymes______________.
a) follow Michaelis-Menton kinetics
b) show hyperbolic plots when plotting [S] versus Vo
c) are monomeric proteins
d) none of the above
122)
Cellulose ______________.
a) is formed from beta-1,4 linked glucose residues
b) is formed from beta-1,6 linked glucose residues
c) is formed from alpha-1,4 linked glucose residues
d) is formed from beta-1,4 linked N-acetyl-glucosamine residues
123)
The kinetic data from an enzyme catalyzed reaction is given below.
a) (10 points) From this information determine the Km’s and Vmax’s for the enzyme
by plotting the data on a Lineweaver Burk (double reciprocal) plot and calculating the
values for Km and Vmax. Label X-axis and Y-axis with correct title and units.
b) (5 points) On the same graph, plot a dashed line that would show graphically how
the addition of a non-competitive inhibitor would effect the Vmax and Km.
c) (5 points) Briefly describe in words (two sentences would be enough) how the
addition of a competitive inhibitor would effect the Vmax and Km.
[S]
Vo
(μmoles/L)
(μmoles/minute)
1.5
0.21
2.0
0.24
3.0
0.28
4.0
0.33
8.0
0.40
16.0
0.45
Use the grid provided and show your work for partial credit.
12
11
10
9
8
7
6
Y Axis
5
4
3
2
1
0
-1
-2
-3
-4
-0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
0
0.1
X Axis
0.2
0.3
0.4
0.5
0.6
0.7
124)
(10 points) Draw the Fischer and Haworth projections for alpha-Dglucose. Circle the anomeric carbon. Make sure to include all hydrogens and
hydroxyl groups. Determine the number of possible stereoisomers for both the
open chain and cyclized forms.
Short answer (5 points each) You are required to answer 4 questions. You may
answer a 5th question for extra credit. Please be complete, but BRIEF!!!!! I will not
grade more than 5 answers. So circle the question number to make sure it is clear
which questions you want me to grade.
125)
Below are the structures the disaccharides of sucrose and maltose. Tell me
which of these two is not a reducing sugar and why you chose this answer.
CH2OH
Sucrose
H
Maltose
O H
OH
O H
H
H
OH
H
O
OH
OH
OH
O
CH2OH
O
H
OH
CH2OH
H
OH
H
OH
H
O
OH
H
CH2OH
CH2OH
H
H
H
OH
H
OH
126)
Vmax = Kcat [total enzyme]. Using the Vmax determined in question 26 and
given that the total enzyme concentration used in the experiments above is 5.0 X
10-3 μM, determine how much time it take for a single reaction to occur? (show
work for partial credit).
127)
List four limitations of the Michaelis-Menton Model of enzyme kinetics.
Why do polysaccharides like chitin and cellulose form linear strands while
128)
polysaccharides like glycogen and starch form helical structures?
129)
Why does the relief of the allosteric inhibition of an enzyme occur in a
faster time frame than relief of inhibition of an enzyme that is inhibited by a
reversible covalent modification?
130)
Although cholesterol is required for life, persons with high serum
cholesterol are at risk of cardiovascular disease. Physicians treat such persons
with inhibitors of the enzyme HMG-CoA reductase, the enzyme that controls
cholesterol synthesis. You are a chemist at a drug company and have just
discovered a chemical that binds irreversibly to HMG-CoA reductase and inhibits
its activity. You describe your discovery to the FDA and they immediately reject
the compound for human use. Why do you think they came up with this decision?
131)
Under physiological conditions, the cellular concentration of most
substrates is below the enzymes Km for that substrate. Under these conditions, at
what velocities is the enzyme functioning? What, if any, metabolic advantage is
realized by cells having these substrate concentrations?
BCH 400/600
Exam 2
March 2, 2006
Name________________________
For questions 1 through 30 mark the correct answer on the provided scantron answer
sheet and on this exam.
Multiple Choice Questions (2 points per question)
1) Which of the following is a property of a catalyst?
a. A catalyst can alter the equilibrium of a chemical reaction.
b. A catalyst is changed to a different form at the end of a reaction.
c. A catalyst can increase the rate of a chemical reaction.
d. a and c
e. all of the above
2) Which of the following classes of enzymes utilize the coenzyme NAD(P)H?
a. Lyases
b. Transferases
c. Oxidoreductases
d. Isomerases
e. Hydrolases
3) Which of the following classes of enzymes catalyze intramolecular rearrangements?
a) Lyases
b) Transferases
c) Oxidoreductases
d) Isomerases
e) Hydrolases
4) Which of the following classes of enzymes catalyze the removal or addition of a
chemical group in reactions involving the rearrangement of electrons?
a) Lyases
b) Transferases
c) Oxidoreductases
d) Isomerases
e) Hydrolases
5) Which of the following classes of enzymes undergoes Ping Pong kinetics?
a) Lyases
b) Transferases
c) Oxidoreductases
d) Isomerases
e) Hydrolases
6) To which of the following classes of enzymes do kinases belong?
a) Lyases
b) Transferases
c) Oxidoreductases
d) Isomerases
e) Hydrolases
7) Enzymes increase the velocity of a reaction by___________________.
a) increasing the ground state energy of the substrate by forming the ES complex
b) stabilizing the formation of the transition state
c) altering the equilibrium of the reaction
d) a and b
e) all of the above
8) Reaction order describes which of the following.
a) The order that substrates bind to the enzyme.
b) The order of reactions in a biosynthetic pathway
c) How the velocity of a reaction is dependent on the concentration of specific
reactants.
d) All of the above
e) a and c
9) Vmax ______________________.
a) describes the velocity of reaction when substrate is bound to ½ of the available
substrate binding sites on an enzyme
b) describes the velocity of reaction when all of the available substrate binding sites
on an enzyme are occupied by substrate
c) is a rate constant for the reaction where the ES complex is converted to the E + P
d) is the value equal to one over the x intercept of a Lineweaver Burk plot.
e) b and d
10) Which of the following types of reactions will result in a hyperbolic plot when [S] is
plotted versus initial velocity?
a) allosterically regulated reactions
b) multi-step reactions
c) Michaelis Menton reactions
d) a and c
e) all of the above
11) Which of the following kinetic parameters can be determined through a Lineweaver
Burk plot?
a) Vmax
b) Km
c) Kcat
d) a and b
e) all of the above
12) Which of the following kinetic parameters best describes the ability of a specific
substrate to bind to a specific enzyme?
a) Vmax
b) Km
c) Kcat
d) Kcat/Km
e) all of the above
13) Cleland notations are used to graphically depict _______________________.
a) allosteric enzyme kinetics
b) the binding order of substrates and the release order of products in a
multisubstrate reaction
c) inhibition kinetics
d) Michaelis Menton kinetics
e) None of the above
14) Which of the following types of reactions involve a covalently modified enzyme
intermediate?
a) random sequential reactions
b) ordered sequential reactions
c) ping-pong reactions
d) a and b
e) none of the above
15) ________________ can bind to the free enzyme.
a) A competitive inhibitor
b) A uncompetitive inhibitor
c) A non-competitive inhibitor
d) a and c
e) b and c
16) _____________ alters the Vmax of an enzyme.
a) A competitive inhibitor
b) A uncompetitive inhibitor
c) A non-competitive inhibitor
d) a and c
e) b and c
17) _____________ binds to the enzyme at sites other than the substrate binding site.
a) An allosteric inhibitor
b) A uncompetitive inhibitor
c) A non-competitive inhibitor
d) a and c
e) all of the above
18) An allosteric activator that affects Km but not Vmax does so by_____________.
a) altering enzyme conformation to promote substrate binding
b) altering enzyme conformation to increase Kcat
c) altering enzyme conformation to prevent binding of a competitive inhibitor
d) altering enzyme conformation to prevent E+PÆES
e) None of the above
19) Which type of regulation occurs in the slowest time frame?
a) regulation through covalent modification
b) allosteric regulation
c) new synthesis of enzyme through gene induction
d) feedback regulation
e) none of the above
20) When oxygen binding changes the conformation of hemoglobin from the T to the R
form it does so in manner consistent with the ___________ model for allosteric
activation.
a) Sequential
b) concerted
c) none of the above
21) When you plot [S] versus initial velocity for an allosteric enzyme, what type of plot
arises?
a) hyperbolic
b) sigmoidal
c) linear
d) discontinuous
e) exponential
22) Enzymes typically have _______ affinity for the substrate than for the transition state.
a) lower
b) higher
c) the same
d) none of the above
23) Which of the following factors contribute to the elevation of the ground state energy
of a substrate once it binds to the enzyme?
a) less favorable entrophy values
b) favorable charge-charge interactions
c) interactions between polar functional groups on the substrate surface and
hydrophobic amino acids in the enzyme’s substrate binding site.
d) a and b
e) a and c
24) Which of the following cofactors is a cosubstrate?
a) pyridoxal phosphate
b) biotin
c) thiamin pyrophophosphate
d) lipoamide
e) NAD(P)H
25) Which of the following cofactors is able to bind CO2 and transfer it to an appropriate
acceptor molecule?
a) pyridoxal phosphate
b) biotin
c) thiamin pyrophophosphate
d) lipoamide
e) NAD(P)H
26) Avidin, a protein found in egg whites binds tightly to which cofactor?
a) pyridoxal phosphate
b) biotin
c) thiamin pyrophophosphate
d) lipoamide
e) NAD(P)H
27) Pairs of isomers that have opposite configurations at only one chiral center are
________.
a) diastereomers
b) enantiomers
c) epimers
d) none of the above
28) The anomeric carbon ______________________.
a) is chiral in a Fisher projections of monosaccharides
b) is chiral in Haworth projections of monosaccharides
c) is the most oxidized carbon in a monosaccharide
d) a and c
e) b and c
29) Reducing sugars _____________________.
a) are monosaccharides in the cyclized form
b) are monosaccharides in the linear form
c) contain hydroxyl groups that can reduce Cu2+ and Ag+
d) a and b
e) a and c
30) When glucose forms a five membered ring, it is designated as a __________.
a) pyranose sugar
b) furanose sugar
c) hexulose sugar
d) none of the abov
31) The kinetic data from an enzyme catalyzed reaction is given below.
a. (5 points) Using the data in the table below, graph the correct Lineweaver
Burk (double reciprocal) plot using the graph paper provided. Label the x
and y axis with the correct units.
b. (5 points) From the Lineweaver-Burk plot, determine the Km and Vmax
of the enzyme. Show your work for partial credit.
c. (5 points) On the same graph, plot a dashed line that would show
graphically how the addition of a non-competitive inhibitor would effect
the Vmax and Km.
d. (5 points) Briefly describe in words what is happening to Km and Vmax
in question 31c.
[S] (μmoles/L)
Vo (μmoles/minute)
0.1
0.2
0.5
0.8
1.0
2.0
3.33
5.00
7.14
8.00
8.33
9.09
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
-6 -4 -2
0
2
4
6
8
10
32
H
O
C
33
NH2
N
O
H2
C
O
34
PO2-
OH OH
NH2
O
N
PO2-
N
O
CH2
O
N
OH OPO3-
35
(2.5 points each) Fill in the blank with the correct cofactor name corresponding to the
figure above. Circle the functional group on the figures above for each coenzyme.
36)_____________________________
37)______________________________
38)______________________________
39)______________________________
N
Questions 40 through 45. Short Answer (5 points each) You are required to answer 2
questions. You may answer a 3rd question for extra credit. I will not grade more than 3
questions so make sure to circle the questions that you want me to grade.
40) The enzyme hexokinase catalyzes a multisubstrate reaction (Glucose + ATP Æ
Glucose-phosphate + ADP). This enzyme undergoes Ping-Pong kinetics. Draw out the
correct Cleland Notation diagram for this reaction.
41) Describe why the value Kcat/Km is a better predictor of the enzymes ability to use a
specific substrate than Km.
42) Why does the Km decrease when an enzyme is treated with an uncompetitive
inhibitor?
43) Draw the Fisher and Haworth (only the furnose form) projection for beta-D-fructose.
Circle the anomeric carbon.
44) Describe the difference between a metalloenzyme and a metal activated enzyme.
45) All serine proteases contain the three amino acid residues, aspartic acid, serine and
histidine, and these amino acids are position in the exact same conformation. Since this
is true, why do trypsin and chymotrypsin have such different substrate specificity? What
features of the enzyme allow for this situation?