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Spr2018_Final_Exam_Answer_Key__1_.docx.docx-Biology 2600: Introduction to Cell Bio
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Spr2018_Final_Exam_Answer_Key__1_.docx.docx-Biology 2600: Introduction to Cell Bio
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Spr2018_Final_Exam_Answer_Key__1_.docx.docx-Biology 2600: Introduction to Cell Bio
Page 14
60.
Investigators are studying a signaling pathway in which an RTK activates the monomeric GTPase Ras.
They discover two new proteins, A and B, have a role in this signaling pathway: cells in which either of
these proteins is disabled by mutation no longer show a response to the signal molecule that binds to the
RTK. To determine the order in which these proteins act, investigators introduce a continuously active
form of Ras into each mutant cell line and record whether this treatment restores signaling.
Cell Line
Signal Molecule
Cell Response
Wild type
-
-
Wild type
+
+
Mutant protein A
-
-
Mutant protein A
+
-
Mutant protein B
-
-
Mutant protein B
+
-
Mutant protein A + overactive Ras
-
+
Mutant protein A + overactive Ras
+
+
Mutant protein B + overactive Ras
-
-
Mutant protein B + overactive Ras
+
-
Based on the results, shown in the table above, which of the following best represents the signaling
pathway under investigation?
a.
RTK → protein A → protein B → Ras →→
b.
RTK → protein A → Ras → protein B →→
c.
RTK → protein B → Ras → protein A →→
d.
RTK → Ras → protein A → protein B →→
61.
Which of the following statements is true?
a.
All enzyme-coupled receptors have an intrinsic catalytic domain on the cytosolic side of the
plasma membrane.
b.
Each extracellular signal molecule interacts with a single class of cell-surface receptor.
c.
G-protein–coupled receptors are GTP-binding proteins.
d.
Ion-channel-coupled receptors can rapidly alter the membrane potential in response to signal
binding.
62. Ligands are signaling molecules that bind to receptors. Which of the following statements is NOT
true
of ligands?
a.
The binding of a ligand to a receptor molecule often causes the receptor to change conformation.
b.
Not all ligands are proteins.
c.
A ligand might bind to more than one specific receptor.
d.
Extracellular ligands never enter the cell.


Page 15
63. You are interested in further understanding the signal transduction pathway that controls the production
of Pig1, a protein important for regulating cell size. Activation of the TRK receptor leads to activation of
the GTP-binding protein, Ras, which then activates a protein kinase that phosphorylates the SZE
transcription factor. SZE only interacts with the nuclear transport receptor when it is phosphorylated.
SZE is a gene activator for the
Pig1
gene. This pathway is diagrammed in the figure below.
Normal cells grown under standard conditions (without ligand) are 14 μm in diameter while normal cells
exposed to TRK ligand are 10.5 μm in diameter. Given this situation, which of the following conditions
do you predict will more likely lead to smaller cells
?
a.
addition of TRK ligand and a drug that stimulates the GTPase activity of Ras
b.
addition of TRK ligand and a drug that inhibits the activity of the phosphatase that acts on SZE
c.
addition of TRK ligand and a drug that stimulates the degradation of Pig1
d.
addition of TRK ligand and a drug that inhibits Pig1 binding to DNA
64. Which of the following is a major difference between microtubules and actin filaments?
a.
Only one of them has a preferred assembly end.
b.
Only one of them is capable of branching assembly, with the assistance of accessory proteins.
c.
Only one of them has intrinsic structural polarity.
d.
Only one of them is assembled from subunits with bound nucleotide.
e.
Only one of them can associate with motor proteins.


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