PCB3023C Exam 3: Cell Biology 2026 |FGCU
1. Which type of cell signaling involves a signal being released into the
bloodstream to act on distant target cells?
A. Paracrine signaling
B. Autocrine signaling
C. Contact-dependent signaling
D. Endocrine signaling
Answer: D
Rationale: Endocrine signaling uses the circulatory system to transport hormones to
target cells located far away.
2. Which of the following describes the function of a G-protein-coupled receptor
(GPCR)?
A. It acts as a ligand-gated ion channel.
B. It phosphorylates tyrosine residues directly.
C. It functions as a transcription factor.
D. It activates a G-protein upon ligand binding.
Answer: D
Rationale: GPCRs interact with heterotrimeric G-proteins, triggering the exchange of GDP
for GTP on the alpha subunit.
,3. What is the primary role of the enzyme Adenylyl Cyclase in cell signaling?
A. To degrade cAMP into AMP.
B. To convert ATP into cAMP.
C. To phosphorylate target proteins.
D. To release calcium from the ER.
Answer: B
Rationale: Adenylyl cyclase is activated by G-alpha-s and catalyzes the synthesis of the
second messenger cAMP from ATP.
4. Which second messenger is released into the cytosol following the cleavage
of PIP2 by Phospholypase C?
A. Diacylglycerol (DAG)
B. cAMP
C. Inositol 1,4,5-trisphosphate (IP3)
D. cGMP
Answer: C
Rationale: PLC cleaves PIP2 into DAG (which stays in the membrane) and IP3 (which
diffuses into the cytosol).
5. What is the effect of GTP hydrolysis on a tubulin dimer within a microtubule?
A. It promotes polymerization.
B. It leads to dynamic instability and potential shrinkage.
C. It increases the affinity of dimers for each other.
D. It stabilizes the microtubule cap.
Answer: B
Rationale: GTP hydrolysis reduces the binding affinity of tubulin dimers, leading to the
loss of the GTP cap and microtubule depolymerization.
, 6. Which motor protein moves cargo toward the minus end of a microtubule?
A. Kinesin
B. Myosin II
C. Dynein
D. Myosin V
Answer: C
Rationale: Dyneins move toward the minus end (toward the MTOC), while most kinesins
move toward the plus end.
7. Which cytoskeletal filament is the most durable and primarily provides
mechanical strength to cells?
A. Actin filaments
B. Intermediate filaments
C. Microtubules
D. Septins
Answer: B
Rationale: Intermediate filaments, like keratin, are designed to withstand mechanical
stress.
8. In muscle contraction, what causes the release of the myosin head from the
actin filament?
A. Hydrolysis of ATP
B. Binding of ATP
C. Release of Pi
D. Binding of Calcium
Answer: B
Rationale: Binding of a new ATP molecule to the myosin head causes it to release its grip
on the actin filament.
1. Which type of cell signaling involves a signal being released into the
bloodstream to act on distant target cells?
A. Paracrine signaling
B. Autocrine signaling
C. Contact-dependent signaling
D. Endocrine signaling
Answer: D
Rationale: Endocrine signaling uses the circulatory system to transport hormones to
target cells located far away.
2. Which of the following describes the function of a G-protein-coupled receptor
(GPCR)?
A. It acts as a ligand-gated ion channel.
B. It phosphorylates tyrosine residues directly.
C. It functions as a transcription factor.
D. It activates a G-protein upon ligand binding.
Answer: D
Rationale: GPCRs interact with heterotrimeric G-proteins, triggering the exchange of GDP
for GTP on the alpha subunit.
,3. What is the primary role of the enzyme Adenylyl Cyclase in cell signaling?
A. To degrade cAMP into AMP.
B. To convert ATP into cAMP.
C. To phosphorylate target proteins.
D. To release calcium from the ER.
Answer: B
Rationale: Adenylyl cyclase is activated by G-alpha-s and catalyzes the synthesis of the
second messenger cAMP from ATP.
4. Which second messenger is released into the cytosol following the cleavage
of PIP2 by Phospholypase C?
A. Diacylglycerol (DAG)
B. cAMP
C. Inositol 1,4,5-trisphosphate (IP3)
D. cGMP
Answer: C
Rationale: PLC cleaves PIP2 into DAG (which stays in the membrane) and IP3 (which
diffuses into the cytosol).
5. What is the effect of GTP hydrolysis on a tubulin dimer within a microtubule?
A. It promotes polymerization.
B. It leads to dynamic instability and potential shrinkage.
C. It increases the affinity of dimers for each other.
D. It stabilizes the microtubule cap.
Answer: B
Rationale: GTP hydrolysis reduces the binding affinity of tubulin dimers, leading to the
loss of the GTP cap and microtubule depolymerization.
, 6. Which motor protein moves cargo toward the minus end of a microtubule?
A. Kinesin
B. Myosin II
C. Dynein
D. Myosin V
Answer: C
Rationale: Dyneins move toward the minus end (toward the MTOC), while most kinesins
move toward the plus end.
7. Which cytoskeletal filament is the most durable and primarily provides
mechanical strength to cells?
A. Actin filaments
B. Intermediate filaments
C. Microtubules
D. Septins
Answer: B
Rationale: Intermediate filaments, like keratin, are designed to withstand mechanical
stress.
8. In muscle contraction, what causes the release of the myosin head from the
actin filament?
A. Hydrolysis of ATP
B. Binding of ATP
C. Release of Pi
D. Binding of Calcium
Answer: B
Rationale: Binding of a new ATP molecule to the myosin head causes it to release its grip
on the actin filament.
