PCB3023C Exam 3: Cell Biology 2026 – FGCU
1. Which signaling molecule is primarily responsible for the ‘fight or flight’
response by binding to adrenergic receptors?
A. Epinephrine
B. Acetylcholine
C. Insulin
D. Glucagon
Answer: A
Rationale: Epinephrine (adrenaline) binds to adrenergic receptors (GPCRs) to trigger the
rapid mobilization of energy and physiological changes during stress.
2. In the G-protein coupled receptor (GPCR) pathway, what occurs immediately
after a ligand binds to the receptor?
A. The G-protein alpha subunit exchanges GDP for GTP.
B. The G-protein alpha subunit hydrolyzes GTP to GDP.
C. The receptor is degraded by a lysosome.
D. cAMP is converted back to ATP.
Answer: A
Rationale: Ligand binding induces a conformational change in the GPCR, which acts as a
GEF (Guanine nucleotide Exchange Factor) for the G-alpha subunit, causing it to swap GDP
for GTP.
,3. Which second messenger is produced by the enzyme Adenylyl Cyclase?
A. Inositol trisphosphate (IP3)
B. Diacylglycerol (DAG)
C. Cyclic AMP (cAMP)
D. Calcium ions (Ca2+)
Answer: C
Rationale: Adenylyl Cyclase catalyzes the conversion of ATP into cAMP, which then
typically activates Protein Kinase A (PKA).
4. What is the primary function of the enzyme Phospholipase C (PLC)?
A. To phosphorylate tyrosine residues on receptors.
B. To synthesize ATP from ADP.
C. To degrade cAMP into 5’-AMP.
D. To cleave PIP2 into IP3 and DAG.
Answer: D
Rationale: Phospholipase C cleaves the membrane phospholipid PIP2 into two second
messengers: IP3 (soluble) and DAG (membrane-bound).
5. Which of the following is a characteristic of Receptor Tyrosine Kinases (RTKs)?
A. They contain seven transmembrane alpha-helices.
B. They associate with heterotrimeric G-proteins.
C. They form dimers upon ligand binding.
D. They directly activate Adenylyl Cyclase.
Answer: C
Rationale: RTKs typically exist as monomers; ligand binding causes them to dimerize and
cross-phosphorylate their intracellular domains.
, 6. Which protein acts as a molecular switch by cycling between an active GTP-
bound state and an inactive GDP-bound state?
A. Tubulin
B. Actin
C. Ras
D. Calmodulin
Answer: C
Rationale: Ras is a small monomeric GTPase that functions as a critical relay in many
signaling pathways, including the MAP kinase pathway.
7. During microtubule assembly, what is required for the addition of tubulin
dimers?
A. ATP-bound tubulin
B. Calcium-bound tubulin
C. ADP-bound tubulin
D. GTP-bound tubulin
Answer: D
Rationale: Tubulin dimers must be bound to GTP to be added to the growing (+) end of a
microtubule. Hydrolysis of GTP to GDP leads to instability.
8. Which motor protein is responsible for retrograde transport (moving toward
the minus end) along microtubules?
A. Myosin II
B. Kinesin
C. Dynein
D. Tropomyosin
Answer: C
Rationale: Dyneins move toward the minus end (usually the centrosome), while most
kinesins move toward the plus end (cell periphery).
1. Which signaling molecule is primarily responsible for the ‘fight or flight’
response by binding to adrenergic receptors?
A. Epinephrine
B. Acetylcholine
C. Insulin
D. Glucagon
Answer: A
Rationale: Epinephrine (adrenaline) binds to adrenergic receptors (GPCRs) to trigger the
rapid mobilization of energy and physiological changes during stress.
2. In the G-protein coupled receptor (GPCR) pathway, what occurs immediately
after a ligand binds to the receptor?
A. The G-protein alpha subunit exchanges GDP for GTP.
B. The G-protein alpha subunit hydrolyzes GTP to GDP.
C. The receptor is degraded by a lysosome.
D. cAMP is converted back to ATP.
Answer: A
Rationale: Ligand binding induces a conformational change in the GPCR, which acts as a
GEF (Guanine nucleotide Exchange Factor) for the G-alpha subunit, causing it to swap GDP
for GTP.
,3. Which second messenger is produced by the enzyme Adenylyl Cyclase?
A. Inositol trisphosphate (IP3)
B. Diacylglycerol (DAG)
C. Cyclic AMP (cAMP)
D. Calcium ions (Ca2+)
Answer: C
Rationale: Adenylyl Cyclase catalyzes the conversion of ATP into cAMP, which then
typically activates Protein Kinase A (PKA).
4. What is the primary function of the enzyme Phospholipase C (PLC)?
A. To phosphorylate tyrosine residues on receptors.
B. To synthesize ATP from ADP.
C. To degrade cAMP into 5’-AMP.
D. To cleave PIP2 into IP3 and DAG.
Answer: D
Rationale: Phospholipase C cleaves the membrane phospholipid PIP2 into two second
messengers: IP3 (soluble) and DAG (membrane-bound).
5. Which of the following is a characteristic of Receptor Tyrosine Kinases (RTKs)?
A. They contain seven transmembrane alpha-helices.
B. They associate with heterotrimeric G-proteins.
C. They form dimers upon ligand binding.
D. They directly activate Adenylyl Cyclase.
Answer: C
Rationale: RTKs typically exist as monomers; ligand binding causes them to dimerize and
cross-phosphorylate their intracellular domains.
, 6. Which protein acts as a molecular switch by cycling between an active GTP-
bound state and an inactive GDP-bound state?
A. Tubulin
B. Actin
C. Ras
D. Calmodulin
Answer: C
Rationale: Ras is a small monomeric GTPase that functions as a critical relay in many
signaling pathways, including the MAP kinase pathway.
7. During microtubule assembly, what is required for the addition of tubulin
dimers?
A. ATP-bound tubulin
B. Calcium-bound tubulin
C. ADP-bound tubulin
D. GTP-bound tubulin
Answer: D
Rationale: Tubulin dimers must be bound to GTP to be added to the growing (+) end of a
microtubule. Hydrolysis of GTP to GDP leads to instability.
8. Which motor protein is responsible for retrograde transport (moving toward
the minus end) along microtubules?
A. Myosin II
B. Kinesin
C. Dynein
D. Tropomyosin
Answer: C
Rationale: Dyneins move toward the minus end (usually the centrosome), while most
kinesins move toward the plus end (cell periphery).
