Download Chem 352 - Fall 2014 - Exam II

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Chem 352 - Fall 2014 - Exam II
Some potentially useful information:
pKa values for ionizable groups in proteins: (α-carboxyl, 2.9; α-amino, 8.3; Asp side chain, 3.9, Glu
side chains, 4.2; His side chain, 6.8; Cys side chain, 9.2; Tyr side chain, 10.1; Lys side chain, 10.7;
Arg side chain, 12.3)
Ideal gas law constant (R) = 8.314 J/(mol•K) = 0.08206 (L•atm)/(mol•K)
Faraday’s constant (F ) = 9.646 x 104 J/(mol•V)
1. One of the steps in the citric acid cycle is the conversion of L-malate to oxaloacetate, a reaction that
is catalyzed by the enzyme malate dehydrogenase:
In an experiment carried out at 20°C in the presence of 2.0 nM malate dehydrogenase to observe the
kinetics of this reaction with varying concentrations of L-malate, the catalytic rate constant was
observed to be 49/s and the KM was observed to be 251 µM.
a. What was the observed Vmax for this reaction under these conditions? ___________
(Show your calculations.)
b. What is the turnover number for malate dehydrogenase under these conditions? _______________ (Show your calculations.)
c. What class of enzyme does malate dehydrogenase belong to? ______________________
d. Under the conditions described above, does malate dehydrogenase display “catalytic perfection”
(Show your calculations.)
e. When an enzyme displays “catalytic perfection”, what physical constraint has been placed on the
enzyme’s ability to further increase the rate of the reaction.
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Chem 352
Exam II
Fall, 2014
f. Using the axes drawn below, sketch the expected Lineweaver-Burke for this experiment. (Be sure
to label your axes, including units)
80
70
60
-3
50
x10
40
30
20
10
-10
-8
-6
-4
-2
0
2
4
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12
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g. Adenosine diphosphate ribose is an uncompetitive inhibitor of malate dehydrogenase. In the
presence of a 1.0 mM concentration of this inhibitor, the Vmax was cut in half. On the graph above,
sketch the observed results.
h. Explain where on the enzyme, relative to the substrate, is this inhibitor likely binding to?
2. Draw the structure of the phospholipid phosphotidylcholine containing a palmityl (16:0) acyl group at
the C1 position a linoleyl (18:2, cis-Δ9,12 ) acyl group at the C2 position.
a. In a couple of sentences, describe the structure that forms spontaneously when
phosphotidylcholine is mixed with water. Include in this description a mention of the
intermolecular interactions that lead to the formation of this structure.
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Chem 352
Exam II
Fall, 2014
3. Below is a figure illustrating the active site of an enzyme found in the glycolytic pathway. The
enzyme catalyzes the following reaction,
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2
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a. What class of biological molecule, e.g., amino acid, carbohydrate, lipid, etc. does the product of
this reaction belong to? ________________________
b. What is the name of the substrate in this reaction? _________________________
c. What class does this enzyme belong to? _______________________________
d. What catalytic mode does His 95 play in step 1 of this reaction? ___________________
e. What catalytic role does Glu 165 play in step 1 of this reaction? ______________________
4. Why are some sugars considered reducing sugars while others are not?
a. Draw and label the structure of a disaccharide that is not a reducing sugar.
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Chem 352
Exam II
Fall, 2014
5. Lactose permease is an integral membrane
protein that transports lactose across
bacterial cell membranes along with
hydrogen ions. The transport cycle is shown
in the diagram to the right.
a. Is this transport uniport, symport or antiport? ________________________
b. Given the membrane potential ΔΨ (Ψin - Ψout) is -55 mV, is the transport of lactose into the cell
favorable at 37°C if the pH is 6.2 and the concentration of lactose is 0.040 mM on the outside of
the cell, when the pH is 7.3 and the concentration of lactose is 0.90 mM on the inside of the cell? _
Explain and show your calculations:
c. If the transport of lactose into the cell is favorable, is the transport active or passive? ___________
Explain
d. If the membrane potential were 0 mV instead of -55 mV, with everything else being the same,
would the transport of lactose into the cell be favorable? _____________________
Explain and show your calculations.
e. What class of biological molecule, e.g., amino acid, carbohydrate, lipid, etc. does lactose belong
to? ____________________
f. Draw the chemical structure for α-lactose.
g. What two monosaccharides comprise lactose?
____________________________________
____________________________________
h. How many chiral carbons does lactose possess? _______________
i. What type of glycosidic bond connects the two monosaccharides? _______________________
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