PCB3023C Cell Biology Exam 3 2026 – FGCU
1. Which motor protein typically moves cargo toward the plus end of a
microtubule?
A. Dynein
B. Myosin II
C. Myosin V
D. Kinesin
Answer: D
Rationale: Most kinesins are plus-end directed motors that transport organelles and
vesicles toward the cell periphery.
2. Which of the following describes the structure of a microtubule?
A. Solid rod made of G-actin
B. Fibrous proteins coiled into cables
C. Hollow tube made of 13 protofilaments
D. Double-stranded helix of F-actin
Answer: C
Rationale: Microtubules are hollow cylinders consisting of 13 parallel protofilaments
made of alpha and beta tubulin heterodimers.
,3. What is the primary role of the Signal Recognition Particle (SRP) in protein
synthesis?
A. Degrading misfolded proteins
B. Assisting in mitochondrial import
C. Directing ribosomes to the endoplasmic reticulum
D. Facilitating nuclear export
Answer: C
Rationale: The SRP recognizes the signal sequence on a nascent polypeptide and brings
the ribosome-mRNA complex to the ER membrane.
4. Which molecule acts as a molecular switch by cycling between a GTP-bound
‘on’ state and a GDP-bound ‘off’ state?
A. Adenylate cyclase
B. Ran GTPase
C. Cyclin-dependent kinase
D. Calmodulin
Answer: B
Rationale: GTPases like Ran, Ras, and Rho act as molecular switches regulated by GEFs
(Guanine Exchange Factors) and GAPs (GTPase Activating Proteins).
5. In the intrinsic pathway of apoptosis, which protein is released from the
mitochondria to trigger the caspase cascade?
A. Bcl-2
B. Caspase-8
C. Cytochrome c
D. Fas ligand
Answer: C
Rationale: Damage to the mitochondria leads to the release of cytochrome c into the
cytosol, where it binds to Apaf-1 to form the apoptosome.
, 6. Which cell junction type connects the actin filaments of one cell to those of a
neighboring cell?
A. Desmosomes
B. Adherens junctions
C. Gap junctions
D. Tight junctions
Answer: B
Rationale: Adherens junctions use cadherins to link the actin cytoskeleton of adjacent
cells, providing mechanical stability.
7. What triggers the activation of G-protein coupled receptors (GPCRs)?
A. Dimerization of the receptor
B. Binding of GTP directly to the receptor
C. Phosphorylation of the intracellular tail
D. Binding of a signal molecule to the extracellular domain
Answer: D
Rationale: GPCRs are activated when a ligand binds to the extracellular portion, causing a
conformational change that allows the receptor to act as a GEF for G-alpha.
8. Which second messenger is produced by the enzyme adenylyl cyclase?
A. IP3
B. DAG
C. cAMP
D. cGMP
Answer: C
Rationale: Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP) in
response to G-protein activation.
1. Which motor protein typically moves cargo toward the plus end of a
microtubule?
A. Dynein
B. Myosin II
C. Myosin V
D. Kinesin
Answer: D
Rationale: Most kinesins are plus-end directed motors that transport organelles and
vesicles toward the cell periphery.
2. Which of the following describes the structure of a microtubule?
A. Solid rod made of G-actin
B. Fibrous proteins coiled into cables
C. Hollow tube made of 13 protofilaments
D. Double-stranded helix of F-actin
Answer: C
Rationale: Microtubules are hollow cylinders consisting of 13 parallel protofilaments
made of alpha and beta tubulin heterodimers.
,3. What is the primary role of the Signal Recognition Particle (SRP) in protein
synthesis?
A. Degrading misfolded proteins
B. Assisting in mitochondrial import
C. Directing ribosomes to the endoplasmic reticulum
D. Facilitating nuclear export
Answer: C
Rationale: The SRP recognizes the signal sequence on a nascent polypeptide and brings
the ribosome-mRNA complex to the ER membrane.
4. Which molecule acts as a molecular switch by cycling between a GTP-bound
‘on’ state and a GDP-bound ‘off’ state?
A. Adenylate cyclase
B. Ran GTPase
C. Cyclin-dependent kinase
D. Calmodulin
Answer: B
Rationale: GTPases like Ran, Ras, and Rho act as molecular switches regulated by GEFs
(Guanine Exchange Factors) and GAPs (GTPase Activating Proteins).
5. In the intrinsic pathway of apoptosis, which protein is released from the
mitochondria to trigger the caspase cascade?
A. Bcl-2
B. Caspase-8
C. Cytochrome c
D. Fas ligand
Answer: C
Rationale: Damage to the mitochondria leads to the release of cytochrome c into the
cytosol, where it binds to Apaf-1 to form the apoptosome.
, 6. Which cell junction type connects the actin filaments of one cell to those of a
neighboring cell?
A. Desmosomes
B. Adherens junctions
C. Gap junctions
D. Tight junctions
Answer: B
Rationale: Adherens junctions use cadherins to link the actin cytoskeleton of adjacent
cells, providing mechanical stability.
7. What triggers the activation of G-protein coupled receptors (GPCRs)?
A. Dimerization of the receptor
B. Binding of GTP directly to the receptor
C. Phosphorylation of the intracellular tail
D. Binding of a signal molecule to the extracellular domain
Answer: D
Rationale: GPCRs are activated when a ligand binds to the extracellular portion, causing a
conformational change that allows the receptor to act as a GEF for G-alpha.
8. Which second messenger is produced by the enzyme adenylyl cyclase?
A. IP3
B. DAG
C. cAMP
D. cGMP
Answer: C
Rationale: Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP) in
response to G-protein activation.
