PCB3023C Exam 3: Cell Biology 2026 |FGCU
1. Which of the following molecules acts as a second messenger in the G-protein
coupled receptor (GPCR) signaling pathway?
A. GDP
B. Adenylate cyclase
C. Cyclic AMP (cAMP)
D. G-alpha subunit
Answer: C
Rationale: cAMP is a common second messenger produced by adenylate cyclase in
response to GPCR activation.
2. Which cytoskeletal filament is responsible for the formation of the contractile
ring during cytokinesis?
A. Microtubules
B. Intermediate filaments
C. Actin filaments
D. Septins
Answer: C
Rationale: Actin filaments, along with myosin motors, form the contractile ring that
pinches the cell into two daughter cells.
,3. Which protein acts as a molecular switch by cycling between an active GTP-
bound state and an inactive GDP-bound state?
A. Kinase
B. Ras protein
C. Phosphatase
D. Cyclin
Answer: B
Rationale: Ras is a small GTPase that functions as a molecular switch in signaling
pathways like the MAP kinase pathway.
4. In the cell cycle, the G1 checkpoint (Start) primarily checks for which of the
following?
A. DNA replication completion
B. Chromosome attachment to spindle
C. Cell size and nutrient availability
D. Proper alignment at the metaphase plate
Answer: C
Rationale: The G1 checkpoint ensures the environment is favorable and the cell is large
enough before committing to DNA synthesis.
5. Which motor protein is typically associated with transport toward the plus (+)
end of microtubules?
A. Dynein
B. Kinesin
C. Myosin II
D. Myosin V
Answer: B
Rationale: Most kinesins move toward the plus end of microtubules, facilitating outward
transport from the cell center.
, 6. The intrinsic pathway of apoptosis is primarily regulated by which organelle?
A. Lysosome
B. Golgi apparatus
C. Mitochondria
D. Endoplasmic reticulum
Answer: C
Rationale: The intrinsic pathway involves the release of cytochrome c from the
mitochondria into the cytosol.
7. Which of the following junctions allows the direct passage of small molecules
and ions between adjacent animal cells?
A. Tight junctions
B. Desmosomes
C. Adherens junctions
D. Gap junctions
Answer: D
Rationale: Gap junctions form channels that allow metabolic and electrical coupling
between cells.
8. A loss-of-function mutation in the p53 gene is most likely to result in:
A. Immediate cell death
B. Uncontrolled cell proliferation
C. Increased DNA repair efficiency
D. Permanent cell cycle arrest
Answer: B
Rationale: p53 is a tumor suppressor; its loss prevents the cell from stopping the cycle to
repair DNA, leading to potential cancer.
1. Which of the following molecules acts as a second messenger in the G-protein
coupled receptor (GPCR) signaling pathway?
A. GDP
B. Adenylate cyclase
C. Cyclic AMP (cAMP)
D. G-alpha subunit
Answer: C
Rationale: cAMP is a common second messenger produced by adenylate cyclase in
response to GPCR activation.
2. Which cytoskeletal filament is responsible for the formation of the contractile
ring during cytokinesis?
A. Microtubules
B. Intermediate filaments
C. Actin filaments
D. Septins
Answer: C
Rationale: Actin filaments, along with myosin motors, form the contractile ring that
pinches the cell into two daughter cells.
,3. Which protein acts as a molecular switch by cycling between an active GTP-
bound state and an inactive GDP-bound state?
A. Kinase
B. Ras protein
C. Phosphatase
D. Cyclin
Answer: B
Rationale: Ras is a small GTPase that functions as a molecular switch in signaling
pathways like the MAP kinase pathway.
4. In the cell cycle, the G1 checkpoint (Start) primarily checks for which of the
following?
A. DNA replication completion
B. Chromosome attachment to spindle
C. Cell size and nutrient availability
D. Proper alignment at the metaphase plate
Answer: C
Rationale: The G1 checkpoint ensures the environment is favorable and the cell is large
enough before committing to DNA synthesis.
5. Which motor protein is typically associated with transport toward the plus (+)
end of microtubules?
A. Dynein
B. Kinesin
C. Myosin II
D. Myosin V
Answer: B
Rationale: Most kinesins move toward the plus end of microtubules, facilitating outward
transport from the cell center.
, 6. The intrinsic pathway of apoptosis is primarily regulated by which organelle?
A. Lysosome
B. Golgi apparatus
C. Mitochondria
D. Endoplasmic reticulum
Answer: C
Rationale: The intrinsic pathway involves the release of cytochrome c from the
mitochondria into the cytosol.
7. Which of the following junctions allows the direct passage of small molecules
and ions between adjacent animal cells?
A. Tight junctions
B. Desmosomes
C. Adherens junctions
D. Gap junctions
Answer: D
Rationale: Gap junctions form channels that allow metabolic and electrical coupling
between cells.
8. A loss-of-function mutation in the p53 gene is most likely to result in:
A. Immediate cell death
B. Uncontrolled cell proliferation
C. Increased DNA repair efficiency
D. Permanent cell cycle arrest
Answer: B
Rationale: p53 is a tumor suppressor; its loss prevents the cell from stopping the cycle to
repair DNA, leading to potential cancer.
