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CHEM 160
Spring 2016
Dr. Fusco-Hernandez
Name:_____________________________
Exam II
1. Both myoglobin and hemoglobin exhibit cooperative binding to oxygen.
a. True
b. False
2. Almost all irreversible enzyme inhibitors bind noncovalently to the enzyme.
a. True
b. Flase
3. Integral membrane proteins can be inserted into the membrane and folded into the normal 3D
structure during translation.
a. True
b. Flase
4. Glyceraldehyde has one chiral carbon so it has two stereoisomers, which are called
diastereomers.
a. True
b. Flase
5. Which of the following statements is FALSE?
a. Hydrogen bonding to a histidine residue assists stabilization of the Fe2+ -O2 complex in
both hemoglobin and myoglobin.
b. Myoglobin is a single polypeptide chain folded about a heme prosthetic group.
c. The iron in both hemoglobin and myoglobin has two coordination sites that bind to
oxygen.
d. Hemoglobin is a tetramer, each of which binds a heme group.
e. In both hemoglobin and myoglobin, iron is chelated by a tetrapyrole ring system.
6. Which of the following observations helps to explain the conformational changes that occur in
hemoglobin upon binding to oxygen?
a. The four heme groups are positioned close to the surface of the molecule.
b. An αβ dimer rotates and slides with respect to the other dimer upon binding oxygen.
c. Neither the heme nor the iron ion in the deoxy conformation is in a planar conformation.
d. All of the above
e. B and C
7. The lock and key model of substrate binding and enzymatic catalysis explains:
a. the release of product.
b. substrate specificity.
c. formation of a transition state.
d. the catalytic mechanism.
e. structural changes that occur on substrate binding.
8. The production of carbon dioxide during respiration in aerobic tissues lowers the pH in
erythrocytes, which in turn ________ the affinity of oxygen binding to hemoglobin.
a. increases
b. decreases
c. has not effect on
9. Which of the following statements BEST describes the Michaelis-Menton constant KM?
a. It is numerically equal to the affinity between the enzyme and its substrate.
b. It is numerically equal to the substrate concentration required to reach half maximal
velocity for an enzyme-catalyzed reaction.
c. It is a measure of the rate of a catalytic process.
d. It is a measure of enzyme efficiency.
e. It has units of concentration.
10. Which of the following statements about inhibitors of enzyme-catalyzed reactions is TRUE?
a. An uncompetitive inhibitor typically affects KM but not kcat.
b. A competitive inhibitor does not affect Vmax.
c. An uncompetitive inhibitor will always bind at the active site.
d. A competitive inhibitor binds irreversibly to the enzyme at the active site.
e. Reversible inhibitors bind to either free enzyme or the enzyme-substrate complex but not
both.
11. Saturated fatty acids are different to unsaturated fatty acids because they:
a. have an even number of carbon atoms.
b. have short hydrophobic tails.
c. have no C=C double bonds.
d. exhibit free rotation about the carbon carbon bonds in the hydrocarbon tail.
e. mostly have cis double bonds.
12. Which of the following is unlikely to be a characteristic of a membrane protein?
a. Largely hydrophobic transmembrane segments
b. α-helical membrane-spanning motifs.
c. Covalently attached lipid moities
d. Symmetric orientation across the membrane
e. β-sheet membrane-spanning motifs
13. Which of the following statements about biological membranes is FALSE?
a. They are composed of a mixture of lipids and proteins in which lateral diffusion of
components is possible.
b. Lipids and proteins move laterally at approximately the same rate within the membrane.
c. The faces of biological membranes are distinct and usually different in both composition
and structure.
d. Phospholipids often require a specialized enzyme to facilitate movement across
(flipping) the membrane.
e. They are often organized into smaller regions of specific function.
14. Which of the following is NOT related to facilitated transport across biological membranes?
a. An ionophore is a carrier protein that increases the permeability of a membrane to ions.
b. Some permeases can transport their substrates in both directions.
c. A symport will transport two molecules in the same direction across a membrane.
d. ATP hydrolysis is required.
e. An antiport will move substrates in opposite directions across a membrane.
15. A common feature of serine proteases is the catalytic triad consisting of a nucleophile, a general
base and an acid. In chymotrypsin these amino acid residues are ______________,
___________________, and _________________ respectively.
16. The _________________ binding of oxygen to hemoglobin is facilitated by changes in protein
conformation upon oxygen binding to one subunit that affect the binding of oxygen to another
subunit.
17. The conserved residues in the hemoglobins and myoglobins include the _______________
proximal and distal to the heme iron.
18. A _________________ inhibitor is one that binds to a place other than the active site of an
enzyme and can be bound to the enzyme with or without the substrate.
19. Active transport can move a substance across a membrane __________________ its
concentration gradient.
20. After a person spends a day or more at high altitude (with an oxygen partial pressure of 75 torr compared
to normally being 100 torr), the concentration of 2,3-biphosphoglycerate in that person’s red blood cells
increases. What effect would an increased concentration of 2,3-BPG have on oxygen-binding curve for
hemoglobin? Explain why this adaptation would be beneficial for functioning well at high altitude. (4
points)
21. Describe the Bohr effect. Make sure to include the effects of both pH and CO2 and the chemical bases for
each. (6 points).
22. Suppose you are studying a protein involved in transporting ions in and out of cells. Would you expect to
find the nonpolar residues in the interior of the exterior? Why? Would you expect to find the polar
residues in the interior or the exterior? Why? (6points)
23. Given the following abbreviations for fatty acids. Which one would you expect to have the lowest
melting point? Why? Which one would you expect to have the highest melting point? Why? (4 points)
a. 16:0
b. 20:0
c. 18:1c9
d. 18:3c9,12,15
24. Triacylglycerols are used for fuel storage in both plants and animals. The triacylglycerols from plants are
often liquid at room temperature, whereas those from animals are solid. Suggest some chemical reasons
for the difference. (3 points)
25. On the following graph label the Km, Vmax, and draw a representation of a competitive inhibitor.
Explain what effect it has on the Km and Vmax and make sure to include why it has this effect. (6 points)
26. Draw a Haworth projection of the six membered ring that is formed from D-glucose. Make sure to
indicate the anomeric carbon and if it is  or . (4 points)
27. Draw a Haworth projection for the disaccharide given the following information (5 points)
a. it is a dimer of glucose (look at question 22)
b. The glycosidic linkage is (1→6)
c. The anomeric carbon not involved in the glycosidic linkage is in the  configuration
28. What is the structural differences that are observed between the difference between an (1→4) and an
(1→4) linkage. Hint think about secondary structures. Make sure to include why one forms one type of
secondary structure and why the other one forms a different type. (4 points)
29. Catalysis of the cleavage of peptide bonds in small peptides by a proteolytic enzyme is described below in
the following table. The arrow indicates the peptide bond cleaved in each case. ( 8points)
Substrate (amino acid sequence)
Km (mM)
Kcat (1/sec)
Kcat/Km
EMTA↓G
4.0
24
6.00
EMTA↓A
1.5
30
20.0
EMTA↓F
0.5
18
36.0
a. If a mixture of these peptides were presented to the enzyme with the concentration of each
peptide being the same, which peptide would be digested most effectively? Least effectively?
Briefly explain your reasoning.
b. The experiment is performed again on another peptide with the following results:
EMTI↓F
9
18
2.00
On the basis of the data, sugeest the features of the amino acid sequence that dictate the
specificity of the enzyme.