Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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1. (1 pt) Write your exam ID (A-1) in the blank at the upper right of your answer sheet.
2. (10 pts) True or False
a. The free energy of the highest-energy intermediate directly determines the rate
of a reaction.
b. KI is equivalent to the Kd of an enzyme-inhibitor complex.
c. Some enzymes are regulated by how much substrate is present.
d. In cumulative feedback inhibition, a pathway product can partially inhibit the
activity of an enzyme in the pathway.
e. In the concerted model of homotropic positive cooperativity, the binding of
substrate yields a higher-affinity (or more active) state of the enzyme.
3. (3 pts) Which one of the following is not true?
a. Enzymes act on and produce specific stereoisomers.
b. Enzymes can be subject to multiple types of regulation.
c. Enzymes function over a wide range of reaction conditions.
d. Enzymes can potentially catalyze many different types of reactions.
e. Enzymes can achieve higher rates of catalysis than chemical catalysts.
4. (10 pts) List all possible results that can be produced by each type of inhibitor:
a. Competitive
b. Mixed
c. Noncompetitive
d. Uncompetitive
Choose from:
1. An apparent decrease in Km
2. An apparent increase in Km
3. No apparent change in Km
4. An apparent decrease in Vmax
5. An apparent increase in Vmax
6. No apparent change in Vmax
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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5. (22 pts) You have discovered a new enzyme, metamorphase, which catalyzes the one-
to-one conversion of caterpillic acid into mothrate. You analyze the kinetics of the
enzyme by combining 0.8 nM metamorphase with varying concentrations of
caterpillic acid, and measuring the rate of production of mothrate, as shown in the
plots below. The equations on each plot describe the dotted line that traces the initial
slope of each curve.
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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(Question 5 continued)
a. Draw a Lineweaver-Burk plot for metamorphase acting on caterpilic acid.
Label the axes with numerical values, labels, and units. Label your line ‘M’.
b. What is the Km of metamorphase for caterpilic acid? Show your work.
c. What is the Vmax of metamorphase in these experiments? Show your work.
d. What is the kcat of metamorphase? Show your work.
e. What is the catalytic efficiency of metamorphase? Show your work.
f. The kinetic experiments with metamorphase are repeated, this time with the
addition of 5 mM frigidol, an inhibitor. The apparent Km and Vmax are 20 mM
and 5 µM/s, respectively. Draw a line representing the results of this
experiment on your plot, and label it ‘M + F’.
g. What type of inhibitor is frigidol (when acting on metamorphase)?
h. What is the KI of the frigidol-metamorphase complex? Show your work.
i. Does metamorphase have a higher affinity for caterpillic acid or frigidol?
(Assume the conversion of caterpillic acid to mothrate is much slower than the
binding and release of caterpillic acid to metamorphase.)
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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6. (15 pts) Below is an enzyme mechanism
(with reaction arrows omitted):
O
OO
OO
HOH2C
CH2OHNH
O
NH
HO
CH
H3C COO-
C O
CH3
CO
CH3
O
OO
OO
CH2OH
CH2OHNH
O
NH
HO
CH
H3C COO-
C O
CH3
CO
CH3
OO
Glu-57
OO
Glu-35
H
OO
Asp-52Enzyme surface
Enzyme surface
HOO
O
CH2OH
NH
HO
CO
CH3
OO
CH2OH
NH
O
CH
H3C COO-
C O
CH3
OO
Glu-57
OO
Glu-35
OO
Asp-52Enzyme surface
Enzyme surface
H2O
H
O
H
OO
Glu-57
OO
Glu-35
H
OO
Asp-52Enzyme surface
Enzyme surface
OO
HOH2C
NH
O
CH
H3C COO-
C O
CH3
OH
a. Name the enzyme.
b. Name the biological substrate
of this enzyme and the
substrate’s function.
c. Name the enzyme class.
d. List, in order, the catalytic
mechanisms used by this
enzyme (in the mechanism
shown).
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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7. (12 pts) Shown below are several O2 binding curves. The curve in bold (#3)
represents O2 binding by red blood cells of an average person living at sea level.
Which curve below best represents O2 binding:
a. For a resident of Tibet, who has a higher-than-average BPG concentration.
b. For an elite athlete, who has a higher-than-average red blood cell count.
c. For an altered hemoglobin that can only adopt the R state.
d. For hemoglobin with half of its binding sites bound by carbon monoxide.
8. (3 pts) What functional groups of hemoglobin bind directly to O2?
9. (7 pts) An alien race on a far-away planet has evolved to resemble earth’s dolphins.
Because of the different air composition, the aliens’ oxygen-binding molecules, called
flipperglobin and goglobin, have different O2 binding affinities and transfer
efficiencies than myoglobin and hemoglobin. Using the information below, draw the
O2 binding curves for these two molecules, and label them ‘G’ for goglobin, and ‘F’
for flipperglobin.
- The pO2 in the aliens’ air-exchange organs is 200 torr.
- The pO2 in the aliens’ internal tissues is 80 torr.
- Goglobin fills 90% of its binding sites in the air-exchange organs, and
transfers oxygen to the tissues with 70% efficiency.
- Flipperglobin, found in the alien’s tissues, has a P50 of 20 torr.
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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10. (4 pts) The ∆G°' of the one-to-one conversion of X to Y is 4.9 kJ/mol. The
concentration of X in human brain cells is 100 µM. At what cellular concentrations
of Y is the conversion of X to Y spontaneous? Show your work.
11. (2 pts) The ∆G°' of the reaction X � 2Z is 7.1 kJ/mol. Write the expression that
relates the ∆G of this reaction in a cell to that of standard conditions.
12. (8 pts) The structure of inorganic phosphate (Pi) is shown:
a. Does Pi act as a nucleophile or electrophile in biochemical
reactions?
b. Briefly explain your answer for part a (15 words or less).
c. The hydrolysis of phosphorylated compounds is generally
spontaneous:
What property of Pi favors this reaction? Briefly explain (15 words or less).
13. (4 pts) A cell has 70% of its adenylates in triphosphate form, 20% in diphosphate
form, and 10% in monophosphate form. Calculate the energy charge in this cell,
showing your work.
P
O
O
OH
O
Chem 153A, Winter 2009, Midterm Exam2, ID: A-1
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Extra Credit – earn up to 5 points
The following reactions occur in bacteria as initial steps in the biosynthesis of certain
amino acids.
For each step (1, 2, 3), list the class and subclass (if applicable) of enzyme that catalyzes
the reaction; choose the corresponding letter from the list provided below. Also, for steps
1 and 2, name the compounds that would most likely fill in the blank boxes. Assume that
the hydrolysis of compound b → a would be favorable in the cell.
C
CH2
O
CH
COO
NH3O
C
CH2
O
CH
COO
NH3O
2-O3P
C
CH2
H
CH
COO
NH3O
CH
CH2
CH2
CH
COO
NH3OH
C
OOC
O
Pi
CH3
C-OOC
O
1
3
2
Choose from:
A. aminotransferase
B. carboxyltransferase
C. dehydrogenase
D. glycosidase
E. hydrolase
F. kinase
G. isomerase
H. ligase
I. lyase
J. mutase
K. oxidase
L. oxidoreductase
M. oxygenase
N. peptidase
O. phosphatase
P. phosphorylase
Q. protease
R. reductase
S. synthase
T. synthetase
U. transferase
V. none of the above
a
b
c
d
Name (Last, First): ______________________________________ First two letters of last name: ___ ___
Student ID Number: ___________________________ Lecture (circle): 9am 12pm
Chemistry and Biochemistry 153A, Winter 2009 Midterm Exam 2, ID:_________
Page 1 (24 points)
2. a. True False
b. True False
c. True False
d. True False
e. True False
3. _____
4. List all that apply:
a. ___________________
b. ___________________
c. ___________________
d. ___________________
Page 1:
Page 3:
Page 4:
Page 5:
Page 3 (22 points)
5. a. & f.
b. d. g. ____________________________
h.
c. e.
i. _____________________________
/ 24
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I have read and agree to all instructions and guidelines for this exam.
Signed: Date:
Total score
/ 15
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Scores
/ 18
Page 6:
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E.C.:
Chemistry and Biochemistry 153A, Winter 2009 Midterm Exam 2
Page 4 (15 points)
6. a. ______________________________________ d.
b. ______________________________________
______________________________________
c. ______________________________________
Page 5 (21 points)
7. a. _____ 9.
b. _____
c. _____
d. _____
8. _______________________________
Page 6 (18 points)
10.
11. _________________________________________
12. a. ______________________________________
b.
c.
13.
E.C. 1. ___________
____________ → ____________
2. ___________
____________ → ____________
3. ___________
(b and c each: 15 words or less)