BIOL 331 PRACTICE EXAM QUESTIONS
& VERIFIED ANSWERS 2026/2027
UPDATE
1. Which of the following describes the function of the Ran-GTPase in nuclear transport?
A. Ran-GTP is high in the nucleus and promotes the dissociation of cargo from importins.
B. Ran-GTP is high in the cytosol and promotes the dissociation of cargo from importins.
C. Ran-GDP is high in the nucleus and promotes the binding of cargo to exportins.
D. Ran-GDP is high in the cytosol and promotes the binding of cargo to importins.
Answer: A
Conceptual Explanation: Ran-GTP is maintained at high concentrations in the nucleus by
Ran-GEF. In the nucleus, Ran-GTP binds to importins, causing them to release their cargo.
Conversely, it promotes cargo binding to exportins.
2. The ‘Power Stroke’ of the myosin motor head is triggered by which event?
A. Release of inorganic phosphate (Pi) from the myosin head.
B. Hydrolysis of ATP to ADP and Pi.
C. Binding of a new ATP molecule to the myosin head.
D. Binding of the myosin head to the actin filament.
,Answer: A
Conceptual Explanation: The power stroke, which involves the conformational change
that moves the actin filament, occurs specifically when inorganic phosphate (Pi) is released
from the myosin head after ATP hydrolysis.
3. Which protein complex is responsible for the nucleation of branched actin filaments?
A. Formin
B. Arp2/3 complex
C. Cofilin
D. Profilin
Answer: B
Conceptual Explanation: The Arp2/3 complex binds to the side of existing actin filaments
and nucleates the growth of a new filament at a 70-degree angle, creating a branched
network.
4. In G-protein coupled receptor (GPCR) signaling, which of the following acts as a Guanine
Nucleotide Exchange Factor (GEF)?
A. The activated receptor
B. The RGS protein (Regulator of G-protein Signaling)
C. The G-alpha subunit itself
D. Adenylate Cyclase
, Answer: A
Conceptual Explanation: Upon ligand binding, the GPCR undergoes a conformational
change that allows it to act as a GEF for the G-alpha subunit, stimulating the exchange of
GDP for GTP.
5. What is the role of the Wee1 kinase in cell cycle regulation?
A. It phosphorylates and activates M-Cdk.
B. It phosphorylates and inhibits M-Cdk.
C. It degrades M-cyclin.
D. It dephosphorylates M-Cdk to trigger entry into mitosis.
Answer: B
Conceptual Explanation: Wee1 is an inhibitory kinase that phosphorylates M-Cdk at
specific sites, keeping the complex inactive until the Cdc25 phosphatase removes these
phosphates.
6. Which mechanism ensures that DNA is replicated only once per cell cycle?
A. Degradation of DNA polymerase in S phase.
B. Phosphorylation and degradation of Cdc6 to prevent re-loading of MCM helicases.
C. Activation of p53 during G2 phase.
D. Binding of Geminin to the ORC complex throughout the entire cell cycle.
Answer: B
& VERIFIED ANSWERS 2026/2027
UPDATE
1. Which of the following describes the function of the Ran-GTPase in nuclear transport?
A. Ran-GTP is high in the nucleus and promotes the dissociation of cargo from importins.
B. Ran-GTP is high in the cytosol and promotes the dissociation of cargo from importins.
C. Ran-GDP is high in the nucleus and promotes the binding of cargo to exportins.
D. Ran-GDP is high in the cytosol and promotes the binding of cargo to importins.
Answer: A
Conceptual Explanation: Ran-GTP is maintained at high concentrations in the nucleus by
Ran-GEF. In the nucleus, Ran-GTP binds to importins, causing them to release their cargo.
Conversely, it promotes cargo binding to exportins.
2. The ‘Power Stroke’ of the myosin motor head is triggered by which event?
A. Release of inorganic phosphate (Pi) from the myosin head.
B. Hydrolysis of ATP to ADP and Pi.
C. Binding of a new ATP molecule to the myosin head.
D. Binding of the myosin head to the actin filament.
,Answer: A
Conceptual Explanation: The power stroke, which involves the conformational change
that moves the actin filament, occurs specifically when inorganic phosphate (Pi) is released
from the myosin head after ATP hydrolysis.
3. Which protein complex is responsible for the nucleation of branched actin filaments?
A. Formin
B. Arp2/3 complex
C. Cofilin
D. Profilin
Answer: B
Conceptual Explanation: The Arp2/3 complex binds to the side of existing actin filaments
and nucleates the growth of a new filament at a 70-degree angle, creating a branched
network.
4. In G-protein coupled receptor (GPCR) signaling, which of the following acts as a Guanine
Nucleotide Exchange Factor (GEF)?
A. The activated receptor
B. The RGS protein (Regulator of G-protein Signaling)
C. The G-alpha subunit itself
D. Adenylate Cyclase
, Answer: A
Conceptual Explanation: Upon ligand binding, the GPCR undergoes a conformational
change that allows it to act as a GEF for the G-alpha subunit, stimulating the exchange of
GDP for GTP.
5. What is the role of the Wee1 kinase in cell cycle regulation?
A. It phosphorylates and activates M-Cdk.
B. It phosphorylates and inhibits M-Cdk.
C. It degrades M-cyclin.
D. It dephosphorylates M-Cdk to trigger entry into mitosis.
Answer: B
Conceptual Explanation: Wee1 is an inhibitory kinase that phosphorylates M-Cdk at
specific sites, keeping the complex inactive until the Cdc25 phosphatase removes these
phosphates.
6. Which mechanism ensures that DNA is replicated only once per cell cycle?
A. Degradation of DNA polymerase in S phase.
B. Phosphorylation and degradation of Cdc6 to prevent re-loading of MCM helicases.
C. Activation of p53 during G2 phase.
D. Binding of Geminin to the ORC complex throughout the entire cell cycle.
Answer: B
