PCB 3023C | PCB3023C Exam 4: Cell Biology
Updated and Latest Questions and Correct
Answers with Rationale - Florida Gulf Coast
University
1. A researcher treats cells with a non-hydrolyzable analog of GTP. Which of the following
effects is most likely to be observed in the GPCR signaling pathway?
A. The G-alpha subunit will remain permanently associated with the G-beta-gamma
complex.
B. The RGS (Regulator of G protein signaling) will accelerate the termination of the signal.
C. The GPCR will be unable to bind its specific extracellular ligand.
D. The G-alpha subunit will remain active and continue to stimulate its effector protein.
Correct Answer: D
Expert Explanation: The correct answer is B because the hydrolysis of GTP to GDP is the
‘off switch’ for G-protein activity. Since the analog cannot be hydrolyzed, the G-alpha
subunit stays in its GTP-bound active conformation. This results in the continuous
stimulation of effector proteins like adenylyl cyclase. Other options are incorrect because
GTP binding triggers dissociation from the beta-gamma complex, not association. This
mechanism highlights the importance of molecular switches in regulating intracellular
communication.
2. Which member of the Bcl-2 family is responsible for forming pores in the outer
mitochondrial membrane to release cytochrome c?
A. Bcl-2
B. Bcl-xL
C. Bax
D. Bad
Correct Answer: C
Expert Explanation: The correct answer is C as Bax and Bak are pro-apoptotic effectors
that oligomerize to form channels. These channels facilitate Mitochondrial Outer
Membrane Permeabilization (MOMP), allowing cytochrome c to escape into the cytosol.
Anti-apoptotic members like Bcl-2 work by inhibiting this pore-forming activity. Without
Bax or Bak, the intrinsic pathway of apoptosis cannot be effectively triggered. This
regulation represents a critical checkpoint in programmed cell death pathways.
,3. Colchicine is a drug that inhibits microtubule polymerization. How would this drug affect
the movement of transport vesicles in a neuron?
A. Vesicle transport would increase due to reduced cytoplasmic viscosity.
B. The direction of vesicle transport would be reversed by dynein motors.
C. Vesicles would move faster by utilizing actin filaments exclusively.
D. Vesicle transport would stop because microtubules serve as the tracks for motor
proteins.
Correct Answer: D
Expert Explanation: The correct answer is B because microtubules provide the essential
structural framework for long-distance intracellular transport. Motor proteins like kinesin
and dynein require intact microtubule tracks to move cargo such as vesicles. If
polymerization is inhibited, the tracks disassemble and transport is halted. Actin-based
transport is typically restricted to the cell periphery and cannot compensate for long
axonal distances. This demonstrates how cytoskeletal dynamics are integral to maintaining
cellular polarity and function.
4. During cellular differentiation, how do master regulatory transcription factors typically
function?
A. By increasing the rate of DNA replication in specialized cells.
B. By causing the permanent deletion of unnecessary genomic DNA.
C. By activating the expression of cell-type-specific genes while inhibiting others.
D. By degrading all existing mRNA transcripts from the undifferentiated state.
Correct Answer: C
Expert Explanation: The correct answer is B because differentiation is driven by selective
gene expression rather than genomic changes. Master regulators like MyoD bind to specific
enhancers to trigger the transcription of specialized proteins. They often work through
positive feedback loops to maintain the differentiated state of the cell. Genomic DNA
remains constant across most cell types, with only the epigenetic landscape changing. This
molecular regulation ensures that cells acquire and keep their unique functional identities.
5. In the MAPK/ERK pathway, what is the immediate consequence of Grb2 binding to a
phosphorylated Tyrosine on an RTK?
A. Grb2 directly phosphorylates Ras.
B. Grb2 recruits SOS, which acts as a GEF for Ras.
C. Grb2 enters the nucleus to activate transcription.
D. Grb2 triggers the degradation of the receptor via the lysosome.
, Correct Answer: B
Expert Explanation: The correct answer is B as Grb2 acts as an adapter protein
connecting the receptor to the GEF. The SH2 domain of Grb2 binds to the phosphotyrosine,
while its SH3 domains bind to SOS. SOS then facilitates the exchange of GDP for GTP on Ras,
activating the downstream cascade. Grb2 itself has no catalytic kinase activity. This
recruitment step is a hallmark of signal transduction following receptor tyrosine kinase
activation.
6. A cell is exposed to a survival factor that activates the Akt (PKB) kinase. How does Akt
primarily prevent apoptosis?
A. By inhibiting the production of ATP within the cell.
B. By directly cleaving and inactivating caspase-3.
C. By increasing the permeability of the mitochondrial membrane.
D. By phosphorylating and inactivating the pro-apoptotic protein Bad.
Correct Answer: D
Expert Explanation: The correct answer is A because Akt promotes cell survival by
neutralizing pro-apoptotic signals. When Bad is phosphorylated by Akt, it is sequestered in
the cytosol by 14-3-3 proteins. This prevents Bad from inhibiting Bcl-2, thereby keeping
the mitochondrial membrane intact. Akt does not have protease activity and thus cannot
cleave caspases directly. This pathway is a major target in cancer research due to its role in
uncontrolled cell growth.
7. Which cytoskeletal component is characterized by its ‘9+2’ arrangement of microtubules in
eukaryotic flagella?
A. Microfilaments
B. Axoneme
C. Intermediate Filaments
D. Basal Body
Correct Answer: B
Expert Explanation: The correct answer is C as the axoneme is the specialized core
structure of cilia and flagella. It consists of nine outer microtubule doublets surrounding
two central singlet microtubules. This arrangement is highly conserved and essential for
the ciliary beating motion driven by dynein. The basal body, by contrast, typically has a 9+0
triplet arrangement. Understanding this structure is key to diagnosing ciliopathies and
movement disorders.
8. Which second messenger is produced when Phospholipase C (PLC) cleaves PIP2?
A. cAMP and PKA
Updated and Latest Questions and Correct
Answers with Rationale - Florida Gulf Coast
University
1. A researcher treats cells with a non-hydrolyzable analog of GTP. Which of the following
effects is most likely to be observed in the GPCR signaling pathway?
A. The G-alpha subunit will remain permanently associated with the G-beta-gamma
complex.
B. The RGS (Regulator of G protein signaling) will accelerate the termination of the signal.
C. The GPCR will be unable to bind its specific extracellular ligand.
D. The G-alpha subunit will remain active and continue to stimulate its effector protein.
Correct Answer: D
Expert Explanation: The correct answer is B because the hydrolysis of GTP to GDP is the
‘off switch’ for G-protein activity. Since the analog cannot be hydrolyzed, the G-alpha
subunit stays in its GTP-bound active conformation. This results in the continuous
stimulation of effector proteins like adenylyl cyclase. Other options are incorrect because
GTP binding triggers dissociation from the beta-gamma complex, not association. This
mechanism highlights the importance of molecular switches in regulating intracellular
communication.
2. Which member of the Bcl-2 family is responsible for forming pores in the outer
mitochondrial membrane to release cytochrome c?
A. Bcl-2
B. Bcl-xL
C. Bax
D. Bad
Correct Answer: C
Expert Explanation: The correct answer is C as Bax and Bak are pro-apoptotic effectors
that oligomerize to form channels. These channels facilitate Mitochondrial Outer
Membrane Permeabilization (MOMP), allowing cytochrome c to escape into the cytosol.
Anti-apoptotic members like Bcl-2 work by inhibiting this pore-forming activity. Without
Bax or Bak, the intrinsic pathway of apoptosis cannot be effectively triggered. This
regulation represents a critical checkpoint in programmed cell death pathways.
,3. Colchicine is a drug that inhibits microtubule polymerization. How would this drug affect
the movement of transport vesicles in a neuron?
A. Vesicle transport would increase due to reduced cytoplasmic viscosity.
B. The direction of vesicle transport would be reversed by dynein motors.
C. Vesicles would move faster by utilizing actin filaments exclusively.
D. Vesicle transport would stop because microtubules serve as the tracks for motor
proteins.
Correct Answer: D
Expert Explanation: The correct answer is B because microtubules provide the essential
structural framework for long-distance intracellular transport. Motor proteins like kinesin
and dynein require intact microtubule tracks to move cargo such as vesicles. If
polymerization is inhibited, the tracks disassemble and transport is halted. Actin-based
transport is typically restricted to the cell periphery and cannot compensate for long
axonal distances. This demonstrates how cytoskeletal dynamics are integral to maintaining
cellular polarity and function.
4. During cellular differentiation, how do master regulatory transcription factors typically
function?
A. By increasing the rate of DNA replication in specialized cells.
B. By causing the permanent deletion of unnecessary genomic DNA.
C. By activating the expression of cell-type-specific genes while inhibiting others.
D. By degrading all existing mRNA transcripts from the undifferentiated state.
Correct Answer: C
Expert Explanation: The correct answer is B because differentiation is driven by selective
gene expression rather than genomic changes. Master regulators like MyoD bind to specific
enhancers to trigger the transcription of specialized proteins. They often work through
positive feedback loops to maintain the differentiated state of the cell. Genomic DNA
remains constant across most cell types, with only the epigenetic landscape changing. This
molecular regulation ensures that cells acquire and keep their unique functional identities.
5. In the MAPK/ERK pathway, what is the immediate consequence of Grb2 binding to a
phosphorylated Tyrosine on an RTK?
A. Grb2 directly phosphorylates Ras.
B. Grb2 recruits SOS, which acts as a GEF for Ras.
C. Grb2 enters the nucleus to activate transcription.
D. Grb2 triggers the degradation of the receptor via the lysosome.
, Correct Answer: B
Expert Explanation: The correct answer is B as Grb2 acts as an adapter protein
connecting the receptor to the GEF. The SH2 domain of Grb2 binds to the phosphotyrosine,
while its SH3 domains bind to SOS. SOS then facilitates the exchange of GDP for GTP on Ras,
activating the downstream cascade. Grb2 itself has no catalytic kinase activity. This
recruitment step is a hallmark of signal transduction following receptor tyrosine kinase
activation.
6. A cell is exposed to a survival factor that activates the Akt (PKB) kinase. How does Akt
primarily prevent apoptosis?
A. By inhibiting the production of ATP within the cell.
B. By directly cleaving and inactivating caspase-3.
C. By increasing the permeability of the mitochondrial membrane.
D. By phosphorylating and inactivating the pro-apoptotic protein Bad.
Correct Answer: D
Expert Explanation: The correct answer is A because Akt promotes cell survival by
neutralizing pro-apoptotic signals. When Bad is phosphorylated by Akt, it is sequestered in
the cytosol by 14-3-3 proteins. This prevents Bad from inhibiting Bcl-2, thereby keeping
the mitochondrial membrane intact. Akt does not have protease activity and thus cannot
cleave caspases directly. This pathway is a major target in cancer research due to its role in
uncontrolled cell growth.
7. Which cytoskeletal component is characterized by its ‘9+2’ arrangement of microtubules in
eukaryotic flagella?
A. Microfilaments
B. Axoneme
C. Intermediate Filaments
D. Basal Body
Correct Answer: B
Expert Explanation: The correct answer is C as the axoneme is the specialized core
structure of cilia and flagella. It consists of nine outer microtubule doublets surrounding
two central singlet microtubules. This arrangement is highly conserved and essential for
the ciliary beating motion driven by dynein. The basal body, by contrast, typically has a 9+0
triplet arrangement. Understanding this structure is key to diagnosing ciliopathies and
movement disorders.
8. Which second messenger is produced when Phospholipase C (PLC) cleaves PIP2?
A. cAMP and PKA
