PCB3023 Exam 2: Molecular Cell Biology Comprehensive Review 2026
|UCF
1. Which of the following describes the function of the Signal Recognition
Particle (SRP) in protein synthesis?
A. It facilitates the folding of proteins in the cytoplasm.
B. It transports mature proteins from the Golgi to the plasma membrane.
C. It acts as a protease to remove the signal peptide.
D. It recognizes and binds to a signal sequence, directing the ribosome to the ER membrane.
Answer: D
Rationale: The SRP binds to the ER signal sequence on a nascent polypeptide and brings
the entire ribosome-mRNA complex to the SRP receptor on the Rough ER membrane.
2. In G-protein coupled receptor (GPCR) signaling, which subunit typically binds
to GTP to become active?
A. Beta subunit
B. Alpha subunit
C. Gamma subunit
D. Delta subunit
Answer: B
Rationale: The alpha subunit of a heterotrimeric G-protein binds GDP in its inactive state
and exchanges it for GTP to become active and dissociate from the beta-gamma complex.
,3. Which secondary messenger is produced by the enzyme Adenylyl Cyclase?
A. cAMP
B. DAG
C. IP3
D. Calcium ions
Answer: A
Rationale: Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP) in
response to G-protein activation.
4. What is the primary role of Ran-GTP in nuclear transport?
A. It phosphorylates nuclear lamins.
B. It binds to the nuclear pore complex to block entry.
C. It triggers the release of cargo from importin in the nucleus.
D. It hydrolyzes ATP to provide energy for mRNA export.
Answer: C
Rationale: High concentrations of Ran-GTP in the nucleus cause importin to release its
cargo protein, facilitating the import process.
5. Dynamic instability in microtubules refers to the alternating cycles of:
A. Growth and shrinkage at the plus end.
B. Translation and transcription.
C. Bending and straightening.
D. Attachment and detachment from the centrosome.
Answer: A
Rationale: Microtubules undergo rapid cycles of polymerization (growth) and
depolymerization (shrinkage) driven by GTP hydrolysis, known as dynamic instability.
, 6. Which motor protein moves cargo toward the minus end of microtubules?
A. Kinesin-1
B. Dynein
C. Myosin II
D. Myosin V
Answer: B
Rationale: Cytoplasmic dyneins are motor proteins that walk toward the minus end
(centrosome) of microtubules, while most kinesins move toward the plus end.
7. Which enzyme is responsible for ‘turning off’ a signal by removing a
phosphate group from a protein?
A. Protein Kinase
B. Phosphorylase
C. GTPase
D. Protein Phosphatase
Answer: D
Rationale: Phosphatases catalyze the removal of phosphate groups from proteins, which
usually reverses the action of kinases.
8. What is the function of the KDEL sequence found on certain proteins?
A. It marks the protein for degradation by the proteasome.
B. It targets the protein to the mitochondria.
C. It ensures the protein is returned to the ER from the Golgi.
D. It signals the protein to be secreted out of the cell.
Answer: C
Rationale: The KDEL C-terminal sequence is a retrieval signal for ER-resident proteins that
have escaped to the Golgi, ensuring they are sent back to the ER via COPI vesicles.
|UCF
1. Which of the following describes the function of the Signal Recognition
Particle (SRP) in protein synthesis?
A. It facilitates the folding of proteins in the cytoplasm.
B. It transports mature proteins from the Golgi to the plasma membrane.
C. It acts as a protease to remove the signal peptide.
D. It recognizes and binds to a signal sequence, directing the ribosome to the ER membrane.
Answer: D
Rationale: The SRP binds to the ER signal sequence on a nascent polypeptide and brings
the entire ribosome-mRNA complex to the SRP receptor on the Rough ER membrane.
2. In G-protein coupled receptor (GPCR) signaling, which subunit typically binds
to GTP to become active?
A. Beta subunit
B. Alpha subunit
C. Gamma subunit
D. Delta subunit
Answer: B
Rationale: The alpha subunit of a heterotrimeric G-protein binds GDP in its inactive state
and exchanges it for GTP to become active and dissociate from the beta-gamma complex.
,3. Which secondary messenger is produced by the enzyme Adenylyl Cyclase?
A. cAMP
B. DAG
C. IP3
D. Calcium ions
Answer: A
Rationale: Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP (cAMP) in
response to G-protein activation.
4. What is the primary role of Ran-GTP in nuclear transport?
A. It phosphorylates nuclear lamins.
B. It binds to the nuclear pore complex to block entry.
C. It triggers the release of cargo from importin in the nucleus.
D. It hydrolyzes ATP to provide energy for mRNA export.
Answer: C
Rationale: High concentrations of Ran-GTP in the nucleus cause importin to release its
cargo protein, facilitating the import process.
5. Dynamic instability in microtubules refers to the alternating cycles of:
A. Growth and shrinkage at the plus end.
B. Translation and transcription.
C. Bending and straightening.
D. Attachment and detachment from the centrosome.
Answer: A
Rationale: Microtubules undergo rapid cycles of polymerization (growth) and
depolymerization (shrinkage) driven by GTP hydrolysis, known as dynamic instability.
, 6. Which motor protein moves cargo toward the minus end of microtubules?
A. Kinesin-1
B. Dynein
C. Myosin II
D. Myosin V
Answer: B
Rationale: Cytoplasmic dyneins are motor proteins that walk toward the minus end
(centrosome) of microtubules, while most kinesins move toward the plus end.
7. Which enzyme is responsible for ‘turning off’ a signal by removing a
phosphate group from a protein?
A. Protein Kinase
B. Phosphorylase
C. GTPase
D. Protein Phosphatase
Answer: D
Rationale: Phosphatases catalyze the removal of phosphate groups from proteins, which
usually reverses the action of kinases.
8. What is the function of the KDEL sequence found on certain proteins?
A. It marks the protein for degradation by the proteasome.
B. It targets the protein to the mitochondria.
C. It ensures the protein is returned to the ER from the Golgi.
D. It signals the protein to be secreted out of the cell.
Answer: C
Rationale: The KDEL C-terminal sequence is a retrieval signal for ER-resident proteins that
have escaped to the Golgi, ensuring they are sent back to the ER via COPI vesicles.
