NAME:__________________
FIRST LAST NAME:__________________
Exam #2
BIO 320
Dr. Chan
There are 35 multiple choice questions worth 2 points each.
Use a #2 pencil to answer the multiple-choice questions.
WRITE YOUR LAST NAME ON THE SCANTRON FORM
There are 5 essay questions worth a total of 30 points.
Use a pen if you want a regrade for essay questions
Write legibly and please do not ramble
1) Which of the following about caveolin is incorrect?
A. caveolin is an intergral membrane protein
B. caveolin is concentrated in membrane rafts
C. caveolin can mediate phagocytosis
D. caveolin can mediate vesicle formation
E. caveolin can medite pinocytosis
2) Clathrin can mediate which of the following type of endocytosis?
A.
B.
C.
D.
E.
Receptor-mediated endocytosis
Pinocytosis
Phagocytosis
A and B
All of the above
3) Which of the following processes are not involved in the endocytosis and sorting of LDL
receptors?
A. Ubiquitination
B. Clathrin-coated pit formation
C. Binding of LDL to LDL receptor
D. Recognition of tyrosine signal on LDL receptor
E. Recognition of mannose-6-phosphate on LDL receptor
4) Mitochondria are the factory for which of the following reactions?
A.
TCA cycle
B.
Electron transport
C.
ATP synthesis
D.
A and B
E.
All of the above
5) Which of the following statements regarding mitochondrial protein translocators and their
functions is/are incorrect?
A.
TOM complex is required for the import of most nucleus-encoded mitochondrial proteins
B.
A single-pass inner membrane protein passes through the TIM23 complex from the
outside in (i.e., starting in the inter-membrane space)
C.
A single-pass inner membrane protein passes through the OXA complex from the
outside in (i.e., starting in the inter-membrane space)
D.
TIM22 complex is required for the insertion of multi-pass inner membrane proteins
E.
TIM23 complex spans both inner and outer mitochondrial membranes
6) Which of the following protein translocator(s) is/are involved in the import of proteins into the
mitochondrial matrix?
A.
TOM
B.
TIM23
C.
OXA
D.
A and B
E.
All of the above
7) Which of the following statements regarding signal sequences is incorrect?
A.
Mitochondrial import signal sequence is generally located near N-terminus of protien
B.
Mitochondrial import signal sequence forms an amphiphilic -helix
C.
Nuclear localization sequence (NLS) and nuclear export sequence (NES) can be both
present on the same protein
D.
E.
Nuclear export sequence (NES) is often rich in leucine
Nuclear localization sequence (NLS) contains FG repeats
8) Which of the following about the nuclear transport system is correct?
A.
Ran-GEF is concentrated in the cytoplasm
B.
All proteins that enter or exit the nucleus contain NLS or NES
C.
Ran-GAP is concentrated in the cytoplasm
D.
Ran is mostly GTP-bound in the cytoplasm
E.
All of the above
9) Which of the following about the nuclear pore complex (NPC) is incorrect?
A.
nuclear pore complex contains subunits that form 8-fold symmetry
B.
nuclear pore complex contains proteins called nucleoporins
C.
the channel is filled by proteins which form a sieve-like gel that excludes large molecules
D.
proteins inside the channel cross-linked to each other by covalent bond
E.
proteins inside the channel cross-link to each other by hydrophobic interaction between
FG repeats
10) Which of the following statements regarding nuclear transport is correct?
A. Ran-GTP disrupts association between nuclear import receptor and import cargo
B. Ran-GDP disrupts association between nuclear import receptor and import cargo
C. Ran-GDP is required for the association of nuclear export receptor and export cargo
D. Nuclear import receptor can bind import cargo only in the presence of Ran
E. The nuclear transport machinery of old and new cells is similarly functional
11) The rate-limiting step of cholesterol biosynthesis is catalyzed by:
A.
HMG-CoA synthase
B.
Prenyl transferase
C.
Decarboxylase
D.
HMG-CoA reductase
E.
Mevalonate kinase
12) Which of the following is the fate of LDL receptor after endocytosis?
A.
recycling
B.
transcytosis
C.
degradation
D.
A and B
E.
All of the above
13) Cholesterol can bind which of the following proteins
A.
Insig
B.
SCAP
C.
SRE-BP
D.
A and B
E.
All of the above
14) When ER to Golgi trafficking is blocked and the level of cholesterol in a cell is low, where
would you find SRE-BP?
A.
Nucleus
B.
Cytosol
C.
Golgi
D.
Mitochondria
E.
ER
15) Cleavage of SRE-BP occurs:
A.
in the Golgi when cholesterol level is low
B.
in the ER when cholesterol level is low
C.
in the Golgi when cholesterol level is high
D.
in the ER when cholesterol level is high
E.
in the nucleus when cholesterol level is low
16) Which of the following is not a common feature of microtubules and microfilaments?
A.
filaments have polarity
B.
assembly rate is subunit concentration-dependent
C.
uses a nucleotide to control assembly/disassembly
D.
nucleation is rate-limiting
E.
hydrolyze ATP to achieve dynamics
17) At critical concentration,
A.
a polymer grows steadily
B.
the assembly of subunits is slower than the disassembly of subunits
C.
the assembly of subunits is faster than the disassembly of subunits
D.
the assembly of subunits is balanced exactly by the disassembly of subunits
E.
there is little assembly or disassembly of subunits
18) The GTP molecule at interface of /-tubulin heterodimer is _______ while the GTP
molecule bound by -tubulin is _______
A.
trapped and stable; hydrolyzable to GDP and exchangeable back to GTP
B.
hydrolyzable to GDP and exchangeable back to GTP; trapped and stable
C.
both are trapped and stable
D.
both are hydrolyzable to GDP and exchangeable back to GTP
E.
none of the above
19) Which of the following about an MTOC is wrong?
A.
MTOC often contains a pair of centrioles
B.
-tubulin ring complexes on the surface of centrosome matrix serve as templates to
nucleate microtubule assembly
C.
-tubulin ring complexes cap the plus end of microtubules
D.
Centriole is a unique microtubule bundle that contains 9 triplet microtubule and each
triplet has 13+10+10 protofilaments
E.
Not all MTOCs have centrioles
20) Which of the following behavior of microtubules is independent of tubulin concentration?
A.
the rate of assembly
B.
the rate of disassembly
C.
frequency of catastrophe
D.
frequency of rescue
E.
none of the above
21) Elongation of microtubules in a test-tube (with pure tubulin preparation) occurs:
A.
ONLY at the + end
B.
ONLY at the end
C.
Equal rates at both ends
D.
Faster at the + end
E.
Faster at the end
22) What is believed to cause rescue of microtubules that are experiencing dynamic instability?
A.
An increase in the concentration of free tubulin
B.
A GEF
C.
The exchange of GDP by GTP within the microtubule lattice
D.
The presence of -tubulin in the microtubule lattice
E.
Islands of GTP-tubulin remaining within the microtubules lattice
23) Which statement regarding motor proteins is wrong?
A. Kinesin-1 (conventional kinesin) moves toward the plus end of microtubule
B. Dynein moves toward the minus end of microtubule
C. Myosin II moves the toward minus end of actin filaments
D. Myosin VI is not involved in muscle contraction
E. Myosin VI moves toward the minus end of actin filaments
24) Which motor can drive the movement of vesicles towards the MTOC?
A. Kinesin-1
B. Dynein
C. Myosin II
D. Myosin V
E. Myosin VI
25) Which of the following statements about kinesin-1 is correct?
A. An ATP-bound globular head binds microtubule tightly
B. An ADP-bound globular head binds microtubule tightly
C. The exchange of ATP for ADP in the leading head causes its neck linker to associate with the
head
D. The exchange of ATP for ADP in the lagging head causes its neck linker to associate with the
head
E. A and C
26) Which motor protein is a non-processive motor?
A. Kinesin-1
B. Dynein
C. Myosin II
D. Myosin V
E. None of the above
27) Which description of actin filament binding proteins is wrong?
A. Arp2/3 complex nucleates actin filament assembly and caps minus end of actin filaments
B. Formin complex nucleates actin filament assembly and caps plus end of actin filaments
C. Thymosin binds G-actin subunits and prevents assembly
D. Profilin binds G-actin subunits and promotes assembly
E. Gelsolin sever actin filament and cap the newly generated plus-end
28) Phosphorylation of myosin II (by light chain kinase) regulates:
A. speed of myosin II
B. processivity of myosin II
C. directionality of myosin II motility
D. association of myosin II molecules with each other
E. association of myosin II molecules with actin filaments
29) Which description about the sarcomere is wrong?
A. CapZ caps plus ends of the actin filaments and anchors them to Z-disc
B. Tropomolulin caps minus ends of actin filaments
C. Titin is an elastic protein that connects thick myosin filaments to Z-disc
D. Nebulin serves as a ruler for length of actin filaments
E. The length of a thick myosin filament gets shorter during muscle contraction
30) Which of the following is not a mechanism for controlling muscle contraction?
A. Action potential activates voltage-gated Ca++ channel on the muscle cell surface
B. extracellular Ca++ enters the cytosol and binds to Ca ++ release channel on the surface of
sarcoplasmic reticulum, causing the release of Ca++ from sarcoplasmic reticulum to the cytosol
C. Ca++ released from the sarcoplasmic reticulum binds Troponin C and changes its
comformation
D. Ca++ released from the sarcoplasmic reticulum binds tropomyosin and changes its
comformation
E. conformation changes lead to exposure of myosin-binding sites on actin
31) Which of the following is correct?
A. Intermediate filaments do not bind nucleoside triphosphate
B.
C.
D.
E.
Intermediate filaments do not have polarity
intermediate filaments are not dynamic
intermediate filaments are stronger than microtubules and actin filaments
All of the above
32) What happens to actin filaments when the concentration of G-actin is above critical
concentration of plus end but below critical concentration of minus end?
A. treadmilling
B. both ends growing
C. both ends shrinking
D. minus end growing while plus end shrinking
E. none of the above
33) In a nonmuscle cell, which protein crosslinks actin filaments to form contractile bundles?
A. profilin
B. -actinin
C. fimbrin
D. cofilin
E. C and D
34) Stathmin cause the disassembling of microtubule by:
A. Binding and sequestering free tubulin subunits
B. Severing microtubule
C. Binding and bending tubulin subunits at the end
D. Accelerating GTP hydrolysis of tubulin subunits
E. Degrading free tubulin subunits
35) MAPs like MAP2 and Tau stabilize microtubule by:
A. Binding along protofilament and bridging the interface between tubulin dimers
B. Increasing the concentration of free tubulin subunit
C. Decelerating GTP hydrolysis of tubulin subunits
D. Binding and blocking disassembling at the end
E. Stabilizing free tubulin subunit
36) What are the key features of a mitochondrial signal sequence and how are these features
used in the mitochondrial import process? (5 points)
Amphipathic (amphiphilic) -helix.
Hydrophobic on one side of helix, which allows signal sequence to bind to hydrophobic
groove of receptor in TOM complex on outer mitochondrial membrane.
Net positive charge on opposite side of helix.
The proton motive force (proton electrochemical gradient or membrane potential) drives
the positively charged signal sequence across the inner mitochondrial membane.
What would happen to the mitochondrial import process when the mitochondrial electron
transport chain is inactivated? Explain your answer. (4 points)
Protons will not be moved out of the mitochondrial matrix.
There will be no proton motive force.
The protein to be imported will be able to pass through the outer membrane but not the
inner membrane.
37) In what ways are the -TuRC and ARP complexes similar and different? (6 points)
Similar:
Both nucleate filament assembly.
Both complexes have subunits that are similar in structure to subunits to be assembled.
Both nucleate filaments from the minus end (allowing growth of filament at plus end).
Both cap minus end of filaments.
Different:
ARP complex associates with side of filament whereas -TuRC does not.
ARP complex most often nucleates filament assembly near plasma membrane, and TuRC does not.
38) You first assembled microtubules with purified tubulin. You then stabilized the microtubules
with taxol before you added fluorescent latex beads that were coated with GTP (and the
GTP did not fall off the beads). Where on the microtubules would you find the latex
beads? Explain your reasoning (and a simple diagram may help you with your answer).
(6 points)
Only at the plus end of microtubules.
-tubulin is exposed at plus end (and -tubulin is exposed at minus end).
Only GTP on -tubulin that is exposed at plus end is free to exchange with GTP that is
not bound to -tubulin already.
When this exchange occurs and involves a GTP molecule that coats the latex bead, the
latex bead will associate with the -tubulin at the exposed plus end.
39) You just learned that the protein examinin has an ER signal sequence near its N-terminal end
and an NLS located near its C-terminal end. For a cell that expresses examinin, where do
you expect to find this protein, and explain your reasoning? (6 points)
Since translocation of a protein into the ER lumen occurs co-translationally, the ER signal
sequence at the N-terminal end of examinin will be recognized by the signal recognition
particle before the C-terminal NLS is synthesized.
Thus, examinin will enter the ER lumen.
If examinin does not have any other signal/sorting sequence, it will be secreted (and not
be found inside a cell).
40) The biosynthetic pathway that leads to the synthesis of cholesterol is important
for the targeting of some proteins in a cell. Show in a simple diagram how
this pathway affects protein targeting. (3 points)
Intermediates (geranyl pyrophosphate and farnesyl pyrophosphate) of this
pathway are needed to modifiy certain proteins (prenylation), thus allowing
such proteins to associate with membranes (as integral membrane proteins).