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Molecular Cell Biology 5068 In Class Exam 2
November 5, 2013
Exam Number: ___________
Please print your name: ______________________________________
Instructions:
Please write only on these pages, in the spaces allotted and not on the back. Write your number on
each page (not your name), so that we can split them up and grade them anonymously. There are a
total of 6 pages including this cover page. You may not use any books or notes, and no electronic
aids, including calculators.
Answer only in the space provided; short, concise answers are preferred and will be rewarded.
Please be as neat as possible.
When you are finished, turn this in to the TA and pick up the take-home portion.
Exam Number:______
MCB 5068 Exam 2 November 4, 2013
Mercer Section (21 points total)
1. Write down 3 functions of tight junctions. (3 points)
2. Hirak takes a urine test and his doctor discovers that he has an abnormally high Mg2+
concentration in his urine. Based upon your knowledge of tight junctions, what gene defect might
he have? (2 points)
3. What plasma membrane adherens junctional protein requires Ca2+ for binding? (1 point)
4. Connexons are “gated” transmembrane protein complexes. If a neighboring epithelial cell is dying
and its cell membrane becomes leaky, the connexons in the adjacent cell will close as a protective
mechanism. Specifically, what does the connexon sense to cause closure? (1 point)
5. In epithelial cells the Na, K-ATPase is generally located on the ________________________________ surface
of the plasma membrane. The Na,K-ATPase transports Na+ (in/out) and K+ (in/out)of the cell. (3
points)
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6. Briefly describe how aquaporins (water channels) in the renal collecting duct respond to
Antidiuretic hormone (ADH) to maintain water homeostasis. (4 points)
7. GPI anchor is a common _________________________________sorting signal. (1 point)
8. Circle all the correct descriptions about the free ion concentrations inside and outside a typical
mammalian cell: (2 points)
a. Intracellular concentration for Na+ and Mg2+ is higher than their extracellular
concentration;
b. Intracellular concentration for K+ and H+ is higher than their extracellular
concentration;
c. Intracellular concentration for Ca2+ is lower than its extracellular concentration;
d. Intracellular concentration for Cl- is lower than their extracellular concentration.
9. Explain the path of a protein from the trans-golgi network(TGN) to the apical surface of the cell via
the indirect sorting pathway. Include in your answer one of the sorting signals known to target for
the apical surface. (4 points)
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Exam Number:______
Colin Nichols Section (21 points)
1. Briefly describe how K+ channels are selective to K+ but not to Na+. (3 points)
2. We discussed two equations that relate membrane potential and ion concentrations:
Goldman-Hogkin-Katz (GHK) equation and the Nernst equation. Which can give a description of
the cellular membrane potential? Give two reasons to explain. (3 points)
3. Write down where the following ion concentration is typically higher (inside or outside of the
cell). (4 points)
-Na+
-K+
-Ca2+
-Cl-
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4. Label what a, b, c, d, and e represent on the graph below: (5 points)
5. Draw a cartoon and give a short description to illustrate the gating states of the Na+ channel states
during all phases of an action potential. (4 points)
6. Briefly explain how KATP channel mutations cause Hyperinsulinemia. (2 points)
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Exam Number:______
Ron Bose Section (18 Points)
1. How does 2D-gel electrophoresis work? Also, give its major limitation. (3 points)
2. Describe three main procedural steps taken to produce a spectrum using a mass spectrometer,
starting with an adequately pure protein sample. (3 points)
3. If you are studying a gene product, what is one major benefit of mass spec over DNA microarray
(2 points)
4. What two early experiments demonstrated the role of Her2 in breast cancer? (2 points)
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5. Beta blockers are used to control heart rate and blood pressure. What family of G-protein coupled
receptors do these compounds target? (2 points)
6. Patients with Chronic kidney disease are given recombinant Erythropoietin (EPO) to prevent
anemia. What family of receptors does EPO bind to? (2 points)
7. Name two major ways protein kinases are regulated. (2 points)
8. What is the function of “DEG” amino acid motif present at the beginning of the PKA activation
loop? (2 points)
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Exam Number:______
Ken Blumer Section (34 points)
1. Describe briefly four modes of cell communication? (4 points)
2. Give names of four classes of cell-surface receptor. (4 points)
3. Name two molecules that can act as second messengers in signal transduction. (2 points)
4. Which subunit of heterotrimeric G-proteins do small G-proteins resemble? (1 point)
5. _________________________________are groups of enzymes responsible for removing phosphate
groups from substrates to inactivate downstream signaling. (1 point)
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6. The following graph was obtained from an experiment performed to investigate insulinspecific receptors on the surface of cells. Describe the experiments performed to obtain
curves A, B, and C? What do they tell? (5 points)
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Exam Number:______
7. What is the function of Regulators of G-signaling (RGS)? Why are they important? (3
points)
8. Briefly describe the mechanism of activation and deactivation cycle of heterotrimeric Gproteins by G- protein coupled receptors. (4 points)
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9. Briefly describe how Receptor Tyrosine Kinases (RTK) work. Also, include two different
mechanisms of dimerization of receptors. (5 points)
10. During EGFR activation of Ras, Grb2 adapter protein plays a crucial role via allostery,
proximity, and covalent modification. Briefly describe what it does? Include in your
description two kinds of interaction domains present in Grb2 and what they bind to? (5
points)
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