PCB3023C Cell Biology Exam 4 - Comprehensive Study Set 2026 –
FGCU
1. Which of the following signaling types involves the release of a signal
molecule into the bloodstream to reach distant target cells?
A. Paracrine signaling
B. Autocrine signaling
C. Endocrine signaling
D. Contact-dependent signaling
Answer: C
Rationale: Endocrine signaling uses the circulatory system to transport hormones or
signals to target cells located far away in the body.
2. Which enzyme is responsible for the conversion of ATP into cyclic AMP
(cAMP) in response to G-protein activation?
A. Phosphodiesterase
B. Phospholipase C
C. Protein Kinase A
D. Adenylyl cyclase
Answer: D
Rationale: Adenylyl cyclase is the membrane-bound enzyme that catalyzes the production
of the second messenger cAMP from ATP.
,3. In the GPCR signaling pathway, which subunit of the G-protein usually
possesses the GTPase activity?
A. Delta subunit
B. Beta subunit
C. Gamma subunit
D. Alpha subunit
Answer: D
Rationale: The alpha subunit binds GTP and has intrinsic GTPase activity, which allows it
to hydrolyze GTP to GDP and turn itself off.
4. Which second messenger is released from the endoplasmic reticulum
following the activation of Phospholipase C?
A. Diacylglycerol (DAG)
B. cAMP
C. Inositol 1,4,5-trisphosphate (IP3)
D. Calcium ions (Ca2+)
Answer: D
Rationale: IP3 binds to receptors on the ER, triggering the release of sequestered Calcium
ions into the cytosol.
5. What is the primary function of a phosphatase in cell signaling?
A. To add a phosphate group to a protein
B. To synthesize ATP
C. To remove a phosphate group from a protein
D. To degrade signal ligands
Answer: C
Rationale: Phosphatases are enzymes that remove phosphate groups, often acting as a
‘switch’ to turn off proteins activated by kinases.
, 6. Which cytoskeletal filament is composed of tubulin heterodimers and exhibits
dynamic instability?
A. Microfilaments
B. Intermediate filaments
C. Septins
D. Microtubules
Answer: D
Rationale: Microtubules are built from alpha and beta tubulin dimers and are known for
their rapid growth and shrinkage, termed dynamic instability.
7. Which motor protein is typically responsible for retrograde transport (moving
toward the minus end) along microtubules?
A. Kinesin
B. Dynein
C. Myosin II
D. Tropomyosin
Answer: B
Rationale: Dyneins move toward the minus end (toward the MTOC), while most kinesins
move toward the plus end.
8. What is the structural arrangement of microtubules in a eukaryotic cilium or
flagellum axoneme?
A. 9 + 0 arrangement
B. Triplet arrangement
C. 9 + 2 arrangement
D. Random bundle
Answer: C
Rationale: The axoneme of cilia and flagella consists of nine outer microtubule doublets
surrounding two central singlet microtubules.
FGCU
1. Which of the following signaling types involves the release of a signal
molecule into the bloodstream to reach distant target cells?
A. Paracrine signaling
B. Autocrine signaling
C. Endocrine signaling
D. Contact-dependent signaling
Answer: C
Rationale: Endocrine signaling uses the circulatory system to transport hormones or
signals to target cells located far away in the body.
2. Which enzyme is responsible for the conversion of ATP into cyclic AMP
(cAMP) in response to G-protein activation?
A. Phosphodiesterase
B. Phospholipase C
C. Protein Kinase A
D. Adenylyl cyclase
Answer: D
Rationale: Adenylyl cyclase is the membrane-bound enzyme that catalyzes the production
of the second messenger cAMP from ATP.
,3. In the GPCR signaling pathway, which subunit of the G-protein usually
possesses the GTPase activity?
A. Delta subunit
B. Beta subunit
C. Gamma subunit
D. Alpha subunit
Answer: D
Rationale: The alpha subunit binds GTP and has intrinsic GTPase activity, which allows it
to hydrolyze GTP to GDP and turn itself off.
4. Which second messenger is released from the endoplasmic reticulum
following the activation of Phospholipase C?
A. Diacylglycerol (DAG)
B. cAMP
C. Inositol 1,4,5-trisphosphate (IP3)
D. Calcium ions (Ca2+)
Answer: D
Rationale: IP3 binds to receptors on the ER, triggering the release of sequestered Calcium
ions into the cytosol.
5. What is the primary function of a phosphatase in cell signaling?
A. To add a phosphate group to a protein
B. To synthesize ATP
C. To remove a phosphate group from a protein
D. To degrade signal ligands
Answer: C
Rationale: Phosphatases are enzymes that remove phosphate groups, often acting as a
‘switch’ to turn off proteins activated by kinases.
, 6. Which cytoskeletal filament is composed of tubulin heterodimers and exhibits
dynamic instability?
A. Microfilaments
B. Intermediate filaments
C. Septins
D. Microtubules
Answer: D
Rationale: Microtubules are built from alpha and beta tubulin dimers and are known for
their rapid growth and shrinkage, termed dynamic instability.
7. Which motor protein is typically responsible for retrograde transport (moving
toward the minus end) along microtubules?
A. Kinesin
B. Dynein
C. Myosin II
D. Tropomyosin
Answer: B
Rationale: Dyneins move toward the minus end (toward the MTOC), while most kinesins
move toward the plus end.
8. What is the structural arrangement of microtubules in a eukaryotic cilium or
flagellum axoneme?
A. 9 + 0 arrangement
B. Triplet arrangement
C. 9 + 2 arrangement
D. Random bundle
Answer: C
Rationale: The axoneme of cilia and flagella consists of nine outer microtubule doublets
surrounding two central singlet microtubules.
