PCB3023C Exam 4: Cell Biology Study Guide 2026 |FGCU
1. Which of the following acts as a molecular switch by cycling between an
active GTP-bound state and an inactive GDP-bound state?
A. G-proteins
B. Protein kinases
C. Cyclin-dependent kinases
D. Adenylyl cyclase
Answer: A
Rationale: G-proteins are classic molecular switches that are ‘on’ when bound to GTP and
‘off’ when bound to GDP.
2. Which cytoskeletal filament is composed of tubulin heterodimers and is
responsible for intracellular transport?
A. Actin filaments
B. Intermediate filaments
C. Myosin filaments
D. Microtubules
Answer: D
Rationale: Microtubules are built from alpha and beta tubulin dimers and serve as tracks
for motor proteins like kinesin and dynein.
,3. During which phase of the cell cycle does DNA replication occur?
A. G1 phase
B. M phase
C. G2 phase
D. S phase
Answer: D
Rationale: The S phase (Synthesis phase) is specifically dedicated to the replication of
nuclear DNA.
4. The enzyme adenylyl cyclase converts ATP into which second messenger?
A. cAMP
B. DAG
C. IP3
D. Calcium ions
Answer: A
Rationale: Adenylyl cyclase catalyzes the cyclization of ATP into cyclic AMP (cAMP), a
major second messenger in GPCR signaling.
5. Which motor protein typically moves toward the minus end of a microtubule?
A. Kinesin
B. Myosin II
C. Dynein
D. Tropomyosin
Answer: C
Rationale: Dyneins are minus-end directed microtubule motors, while most kinesins are
plus-end directed.
, 6. Which family of proteins regulates apoptosis by controlling the release of
cytochrome c from the mitochondria?
A. Bcl-2 family
B. Caspases
C. Cyclins
D. Cadherins
Answer: A
Rationale: The Bcl-2 family includes both pro-apoptotic (e.g., Bax, Bak) and anti-apoptotic
(e.g., Bcl-2) members that regulate mitochondrial membrane permeability.
7. What is the primary role of the p53 protein in the cell?
A. Promoting cell growth
B. Synthesizing the mitotic spindle
C. Enabling the transition from G2 to M phase
D. Acting as a tumor suppressor by halting the cell cycle upon DNA damage
Answer: D
Rationale: p53 is a tumor suppressor that triggers cell cycle arrest or apoptosis in
response to DNA damage.
8. Which signaling molecule diffuses across the membrane to bind to
intracellular receptors?
A. Insulin
B. Nitric Oxide (NO)
C. Glucagon
D. Epidermal Growth Factor (EGF)
Answer: B
Rationale: Nitric oxide is a small, gaseous signaling molecule that can diffuse directly
through the plasma membrane.
1. Which of the following acts as a molecular switch by cycling between an
active GTP-bound state and an inactive GDP-bound state?
A. G-proteins
B. Protein kinases
C. Cyclin-dependent kinases
D. Adenylyl cyclase
Answer: A
Rationale: G-proteins are classic molecular switches that are ‘on’ when bound to GTP and
‘off’ when bound to GDP.
2. Which cytoskeletal filament is composed of tubulin heterodimers and is
responsible for intracellular transport?
A. Actin filaments
B. Intermediate filaments
C. Myosin filaments
D. Microtubules
Answer: D
Rationale: Microtubules are built from alpha and beta tubulin dimers and serve as tracks
for motor proteins like kinesin and dynein.
,3. During which phase of the cell cycle does DNA replication occur?
A. G1 phase
B. M phase
C. G2 phase
D. S phase
Answer: D
Rationale: The S phase (Synthesis phase) is specifically dedicated to the replication of
nuclear DNA.
4. The enzyme adenylyl cyclase converts ATP into which second messenger?
A. cAMP
B. DAG
C. IP3
D. Calcium ions
Answer: A
Rationale: Adenylyl cyclase catalyzes the cyclization of ATP into cyclic AMP (cAMP), a
major second messenger in GPCR signaling.
5. Which motor protein typically moves toward the minus end of a microtubule?
A. Kinesin
B. Myosin II
C. Dynein
D. Tropomyosin
Answer: C
Rationale: Dyneins are minus-end directed microtubule motors, while most kinesins are
plus-end directed.
, 6. Which family of proteins regulates apoptosis by controlling the release of
cytochrome c from the mitochondria?
A. Bcl-2 family
B. Caspases
C. Cyclins
D. Cadherins
Answer: A
Rationale: The Bcl-2 family includes both pro-apoptotic (e.g., Bax, Bak) and anti-apoptotic
(e.g., Bcl-2) members that regulate mitochondrial membrane permeability.
7. What is the primary role of the p53 protein in the cell?
A. Promoting cell growth
B. Synthesizing the mitotic spindle
C. Enabling the transition from G2 to M phase
D. Acting as a tumor suppressor by halting the cell cycle upon DNA damage
Answer: D
Rationale: p53 is a tumor suppressor that triggers cell cycle arrest or apoptosis in
response to DNA damage.
8. Which signaling molecule diffuses across the membrane to bind to
intracellular receptors?
A. Insulin
B. Nitric Oxide (NO)
C. Glucagon
D. Epidermal Growth Factor (EGF)
Answer: B
Rationale: Nitric oxide is a small, gaseous signaling molecule that can diffuse directly
through the plasma membrane.
