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BIOLOGY 103
Spring 2001
MIDTERM
NAME _______KEY____________________
LAB SECTION __________
ID# (last four digits of SS#) ______________
STUDENT PLEASE READ. Do not put yourself at a disadvantage by revealing the content
of this exam to your classmates. Your grade will be determined relative to the overall
performance of the class and you may end up paying a heavy price if you provide
information that may benefit those students taking the exam after you. By writing your
name in this page you agree not to discuss the content of this exam with students who have
not taken the exam. Doing so will not only affect your grade but also will result in
disciplinary action against you.
SELECT THE BEST POSSIBLE ANSWER. (3 points each)
1) An enzyme that phosphorylates a protein is known as
a. pyruvate
b. kinase
c. phosphatase
d. carrier
e. channel
f. none of the above
2) Exposure of a cell to a temperature lower than normal would cause the membrane to
become less fluid because
a. all protein channels cease working
b. all protein carriers cease working
c. all fatty acids become saturated
d. more cholesterol gets deposited in the membrane
e. phospholipids loose their amphipathic properties
f. none of the above
3) The transmembrane region of an ion channel forms an aqueous pore across the lipid
bilayer. Which of the following amino acids would you expect to find forming the inside
of the pore?
a. Leucine and Aspartic Acid
b. Glycine and Serine
c. Tryptophan and Methionine
d. Alanine and Isoleucine
e. Cysteine and Valine
f. Aspartic Acid and Arginine
4) In one sentence, explain your choice of the answer for question 3.
Both amino acids have (charged) polar side chains
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5) A pure lipid bilayer (with no proteins) exhibits which of the following properties?
a. membrane potential
b. simple diffusion
c. active transport
d. passive transport
e. all of the above
f. none of the above
6) This molecule acts as the last electron acceptor of the electron transport chain
a. NADH
b. ubiquinone
c. cytochrome c
d. oxygen
e. glucose
f. ATP
7) In reference to your answer to question 6, how does that molecule enters the
mitochondria?
a. simple diffusion
b. passive transport
c. active transport
d. as pyruvate
e. it does not have to enter the mitochondria because it is produced there
f. none of the above
8) In a phospholipid, fatty acids are linked to this molecule
a. phosphate
b. serine
c. cholesterol
d. glycerol
e. isoprene
f. both (a) and (d) are correct
9) Which part of the phospholipid molecule influences the fluidity of a lipid bilayer?
The hydrophobic fatty acid tails
10) What is keratin?
A cytoplasmic intermediate filament protein
11) Which of the following peptides would you expect to interact with the active site of a
protein kinase?
a. Leucine-Aspartic acid-Threonine-Serine-Alanine-Leucine
b. Leucine-Valine-Glycine-Arginine-Leucine
c. Alanine-Proline-Proline-Proline-Tryptophan
d. Glutamic acid-Lysine-Arginine-Cysteine-Methionine
e. both (a) and (b) are correct
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g. none of the above
12) In one sentence explain your answer to question 11.
Peptide a is the only one that has serine, threonine or tyrosine, the only three
amino acids that can be phosphorylated by a kinase
13) All enzymes function as biological catalysts by
a. decreasing the free energy of an unfavorable reaction so it can occur
spontaneously
b. increasing the free energy of an unfavorable reaction so it can occur
spontaneously
c. creating electrochemical gradients within the active site
d. reducing the activation energy necessary for the reaction to take place
e. increasing the activation energy necessary for the reaction to take place
f. decreasing both the free energy and the activation energy
14) Na+ is commonly used to drive the coupled inward transport of nutrients in animal cells
because
a. a steep concentration gradient (high outside and low inside) is maintained by
the Na+-glucose symport
b. a steep concentration gradient (high outside and low inside) is maintained by
the Na+K+ pump
c. a steep concentration gradient (low outside and high inside) is maintained by
the Na+glucose symport
d. a steep concentration gradient (low outside and high inside) is maintained by
the Na+K+ pump
e. most animals eat processed junk food which is high in salt
15) The three protein complexes of the respiratory chain derived energy from _______ to
pump ________ across the inner mitochondrial membrane
a. phosphorylation … electrons
b. ATP hydrolysis …. protons
c. a Na+ gradient …… K+
d. electrons …. protons
e. protons …… electrons
f. none of the above
16) The transport of a molecule by a protein carrier differs from the transport of a molecule
by a protein channel in that
a. the transport by the channel exhibits saturation kinetics
b. carriers always transport molecules into the cell while channels always
transport molecules out the cell
c. carriers always transport molecules out the cell while channels always
transport molecules into the cell
d. carriers only transport hydrophobic molecules while channels can transport
hydrophobic and hydrophilic molecules
e. both (a) and (b) are correct
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f. none of the above
17) Which of the following statements best defines the function of cholesterol?
a. a carrier of molecules across the lipid bilayer
b. an immediate source of ATP
c. an important regulator of the activity of glycolytic enzymes
d. an important regulator of membrane fluidity
e. all of the above
f. both (a) and (d) are correct
18) Hexokinase, the enzyme that catalyzes the first step in glycolysis, can accept either
glucose or galactose as a substrate. From kinetic experiments you determine that the Km
for galactose is 0.5 mM (millimolar) while the Km for glucose is 50 nM (nanomolar).
Therefore
a. hexokinase has higher affinity for galactose than glucose
b. hexokinase has a higher affinity for glucose than galactose
c. the concentration of glucose in the cell is likely to be approximately 1nM
d. the Vmax is the same for both glucose and galactose
e. both (b) and (d) are correct
g. none of the above
19) For a voltage-gated ion channel, the probability of the channel being open is controlled
by
a. the concentration of the ion outside the cell
b. the concentration of the ion inside the cell
c. the membrane potential
d. binding of a ligand
e. phosphorylation
f. none of the above
20) The primary function of the glucose carrier is
a. the passive import of glucose into the cell
b. the active transport of glucose into the cell
c. the active transport of glucose out of the cell
d. the coupled transport of glucose and protons into the cell
e. the phosphorylation of glucose
f. none of the above
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SELECT FROM AMONG THE FOLLOWING LIST OF TERMS TO ANSWER
QUESTIONS 21-33. Terms may be used more than once or not at all. Only one term per
question. (3 points each)
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
ATP synthase
protein phosphatase
cytochrome c
phosphatidylcholine
cholesterol
Na+K+ATPase pump
saturated fatty acid
unsaturated fatty acid
hexokinase
phosphofructokinase
ATP
l. acetyl CoA
m. ADP
n. pyruvate
o. NADH dehydrogenase
p. stearic acid
q. voltage-gated Na+ channel
r. oxygen
s. NADH
t. K+
u. H+
v. cytochrome oxidase
21) __E___ membrane lipid found only in animal cells
22) __V___ this is the last of the respiratory enzyme complexes that accepts electrons
23) __I___ this enzyme phosphorylates glucose
24) __H__ membranes containing this molecule will be more fluid than membranes which
do not contain this molecule
25) __C__ the only protein of the electron transport chain that is not a proton pump
26) __J___ the activity of this enzyme can be allosterically regulated by the first product of
the citric acid cycle
27) __N___ a three carbon acid that is the final product of glycolysis
28) __L__ entry of this molecule into the Krebs cycle results in the production of citrate
29) __A___ this protein can hydrolyze ATP to pump protons across the membrane
30) __C___ this molecule serves as a mobile carrier that ferries electron from one respiratory
enzyme complex to another respiratory enzyme complex
31) __Q___ allows Na+ to enter the cell in response to a change in membrane potential
32) __F___ responsible for the active export of Na+ from the cell
33) ___T__ the movement of this molecule into and out of the cell is largely responsible for
establishing the resting membrane potential
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TRUE OR FALSE. If false, provide a brief correct answer not to exceed the space
provided. (3 points each)
34) __true____ Animal cells use the Na+ gradient to take up nutrients actively
35) __false____ the oxidation of glucose in the cytosol releases 100% of the total free energy
potentially available from that glucose molecule
the oxidation of glucose to pyruvate releases less than 10% of the total free
energy available in that glucose molecule
36) ___true___ the cytochrome oxidase complex of the respiratory chain has a higher affinity
for electrons than ubiquinone
37) ___true___ The Na+K+ ATPase pump helps maintain the osmotic balance of animal
cells
38) __true___ All intermediate filament proteins have a high content of α-helices
39) ___true__ Intermediate filaments are found in the nucleus as well as the cytoplasm
40) _false___ A competitive inhibitor reduces the Vmax of an enzyme
a competitive inhibitor increases Km and has no effect on Vmax
41) __true___ In a Lineweaver-Burke plot (1/S vs 1/V) the presence of a noncompetitive
inhibitor affects the slope of the line
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42) __true____ Vmax is achieved when all of the enzyme in the reaction is bound to
substrate
43) __false___ All enzymes begin to exhibit a saturation effect at a substrate concentration
that equals Km
saturation effect is evident at very high substrate concentrations
44) __true___ The centrosome is the major microtubule organizing center in cells
45) ___true___ Tubulin dimers have a bound molecule of GTP that is hydrolyzed to GDP
after the tubulin assembles into a microtubule
46) ___true__ By creating a reaction pathway that couples an energetically favorable
reaction to an energetically unfavorable reaction, enzymes cause otherwise
impossible reactions (i.e., those with a +∆G) to occur
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SHORT ANSWERS. Do not exceed the space provided. Please write neatly; if I can’t read
it, I won’t grade it! (4 points each)
47) Dynamic instability refers to the behavior of cytoplasmic microtubules to switch back
and forth between growing and shrinking. Mention two factors that determine whether
the microtubule will be growing or shrinking and explain how these factors affect
microtubule behavior.
Dynamic instability occurs at the plus end and is determined by
the concentration of αβ tubulin dimers and the rate of GTP
hydrolysis. When the concentration of αβ dimers is high, they
will be added to the plus end faster than the rate of GTP
hydrolysis, resulting in a GTP cap that prevents
depolymerization. If the concentration of αβ dimers is low, the
rate of GTP hydrolysis would be faster that then rate of
polymerization and GDP-subunits would depolymerize from
the plus end because of their low affinity to the polymer.
48) Explain how intermediate filaments provide strength to a sheet of epithelial.
Intermediate filaments span from one side of the cell to the opposite site
and are indirectly connected to filaments in neighboring cells through
desmosomes. This results in a continuous network of filaments that
traverses through the entire cell sheet.
49) Explain how the cell utilizes a proton gradient to synthesize ATP.
The electron transport chain generates a proton-motive force
(consisting of a membrane potential and a proton
concentration gradient) across the inner mitochondrial
membrane. The protons flow back into the mitochondrial
matrix through the Fo (transmembrane proton carrier) subunit
of ATP synthase, which harnesses the energy from the proton
gradient to make ATP from ADP and Pi
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