BIOL 331 ADVANCED CELL BIOLOGY
EXAM PREP QUESTIONS & VERIFIED
ANSWERS 2026/2027 UPDATE
1. Which of the following describes the mechanism by which the Signal Recognition Particle
(SRP) halts translation of a nascent polypeptide?
A. SRP binds to the large ribosomal subunit and blocks the A site.
B. SRP induces mRNA degradation before the ribosome reaches the translocon.
C. SRP binds to the signal sequence and the ribosome, interfering with elongation factor
binding.
D. SRP phosphorylates the ribosome to cause reversible dissociation.
Answer: C
Conceptual Explanation: SRP binds to the signal sequence as it emerges from the
ribosome and pauses translation by preventing the binding of elongation factors, ensuring
the protein is not folded before reaching the ER translocon.
2. In the process of nuclear import, what is the specific role of the Ran-GAP protein?
A. It triggers GTP hydrolysis on Ran in the cytosol to release the importin.
B. It facilitates the dissociation of the cargo from the importin receptor.
C. It promotes the exchange of GDP for GTP on Ran in the nucleus.
,D. It acts as a chaperone to guide the Ran-GTP complex through the nuclear pore.
Answer: A
Conceptual Explanation: Ran-GAP (GTPase Activating Protein) is localized in the cytosol
and stimulates Ran to hydrolyze its bound GTP to GDP, which is essential for releasing the
nuclear transport receptor to begin another cycle.
3. Which protein complex is responsible for the translocation of unfolded proteins across the
mitochondrial inner membrane?
A. TIM23 complex
B. TOM complex
C. SAM complex
D. OXA complex
Answer: A
Conceptual Explanation: The TIM23 complex handles the translocation of proteins into
the mitochondrial matrix or their insertion into the inner membrane, while TOM is on the
outer membrane.
4. The ‘Treadmilling’ phenomenon in actin filaments occurs when:
A. The concentration of G-actin is between the Cc of the plus end and the minus end.
B. The critical concentration is higher at the plus end than the minus end.
C. ATP hydrolysis occurs faster than subunit addition at both ends.
, D. Profilin prevents the addition of actin subunits to the minus end.
Answer: A
Conceptual Explanation: Treadmilling occurs when the free actin monomer concentration
is above the Cc for the plus end but below the Cc for the minus end, leading to addition at
the plus end and loss at the minus end.
5. What is the primary function of the Mannose-6-Phosphate (M6P) tag added in the Golgi
apparatus?
A. Targeting proteins to the mitochondrial matrix
B. Marking misfolded proteins for proteasomal degradation
C. Sorting acid hydrolases to lysosomes
D. Directing secretory vesicles to the plasma membrane
Answer: C
Conceptual Explanation: M6P is a chemical marker added to the N-linked
oligosaccharides of soluble lysosomal enzymes in the cis-Golgi, which is recognized by M6P
receptors for trafficking to lysosomes.
6. Which of the following best describes the role of the APC/C (Anaphase-Promoting
Complex/Cyclosome) during the cell cycle?
A. It acts as a ubiquitin ligase that targets Securin and Cyclin B for degradation.
B. It phosphorylates M-cyclin to activate mitosis.
EXAM PREP QUESTIONS & VERIFIED
ANSWERS 2026/2027 UPDATE
1. Which of the following describes the mechanism by which the Signal Recognition Particle
(SRP) halts translation of a nascent polypeptide?
A. SRP binds to the large ribosomal subunit and blocks the A site.
B. SRP induces mRNA degradation before the ribosome reaches the translocon.
C. SRP binds to the signal sequence and the ribosome, interfering with elongation factor
binding.
D. SRP phosphorylates the ribosome to cause reversible dissociation.
Answer: C
Conceptual Explanation: SRP binds to the signal sequence as it emerges from the
ribosome and pauses translation by preventing the binding of elongation factors, ensuring
the protein is not folded before reaching the ER translocon.
2. In the process of nuclear import, what is the specific role of the Ran-GAP protein?
A. It triggers GTP hydrolysis on Ran in the cytosol to release the importin.
B. It facilitates the dissociation of the cargo from the importin receptor.
C. It promotes the exchange of GDP for GTP on Ran in the nucleus.
,D. It acts as a chaperone to guide the Ran-GTP complex through the nuclear pore.
Answer: A
Conceptual Explanation: Ran-GAP (GTPase Activating Protein) is localized in the cytosol
and stimulates Ran to hydrolyze its bound GTP to GDP, which is essential for releasing the
nuclear transport receptor to begin another cycle.
3. Which protein complex is responsible for the translocation of unfolded proteins across the
mitochondrial inner membrane?
A. TIM23 complex
B. TOM complex
C. SAM complex
D. OXA complex
Answer: A
Conceptual Explanation: The TIM23 complex handles the translocation of proteins into
the mitochondrial matrix or their insertion into the inner membrane, while TOM is on the
outer membrane.
4. The ‘Treadmilling’ phenomenon in actin filaments occurs when:
A. The concentration of G-actin is between the Cc of the plus end and the minus end.
B. The critical concentration is higher at the plus end than the minus end.
C. ATP hydrolysis occurs faster than subunit addition at both ends.
, D. Profilin prevents the addition of actin subunits to the minus end.
Answer: A
Conceptual Explanation: Treadmilling occurs when the free actin monomer concentration
is above the Cc for the plus end but below the Cc for the minus end, leading to addition at
the plus end and loss at the minus end.
5. What is the primary function of the Mannose-6-Phosphate (M6P) tag added in the Golgi
apparatus?
A. Targeting proteins to the mitochondrial matrix
B. Marking misfolded proteins for proteasomal degradation
C. Sorting acid hydrolases to lysosomes
D. Directing secretory vesicles to the plasma membrane
Answer: C
Conceptual Explanation: M6P is a chemical marker added to the N-linked
oligosaccharides of soluble lysosomal enzymes in the cis-Golgi, which is recognized by M6P
receptors for trafficking to lysosomes.
6. Which of the following best describes the role of the APC/C (Anaphase-Promoting
Complex/Cyclosome) during the cell cycle?
A. It acts as a ubiquitin ligase that targets Securin and Cyclin B for degradation.
B. It phosphorylates M-cyclin to activate mitosis.
