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BIOD 331
BIOD 331 Module 4 Portage- Pathophysiology
Exam Questions with Correct Verified Answers
Latest Update (2025/2026) Guaranteed Pass
1. How do cyclin levels affect MPF activity?: Cyclin levels
fluctuate throughout the cell cycle; rising cyclin levels activate MPF,
pushing the cell into mitosis.
2. What is the function of the Cdk inhibitor p27?: p27 binds to
Cyclin A-Cdk2, preventing S phase progression. Its degradation allows
the cell to enter S phase.
3. What triggers the end of mitosis?: The end of mitosis is
triggered by a drop in mitotic cyclin levels, achieved through ubiquitin-
mediated proteolysis.
4. How does proteolysis ensure a clean transition between cell
cycle phases?: Proteolysis degrades cyclins to inactivate Cdks,
ensuring that the cell progresses through phases without reversal and
only when ready.
BIOD 331
,5. What is the role of phosphorylation in cell cycle regulation?:
Phosphorylation is a reversible and rapid way to regulate protein
activity, controlling the activation and inactivation of Cdks and their
regulators.
6. What is the function of Cdk-activating kinase (CAK)?: CAK
phosphorylates an activating site on the Cdk, promoting full activation
of the Cdk-cyclin complex.
7. What role does Wee1 kinase play in cell cycle regulation?:
Wee1 kinase adds a phosphate to an inhibitory site on the Cdk,
keeping it inactive even when cyclin is bound, preventing premature
entry into mitosis.
8. What is the function of Cdc25 phosphatase?: Cdc25 removes
the inhibitory phosphate added by Wee1, activating the Cdk-cyclin
complex when the cell is ready to proceed and triggering entry into
mitosis.
9. How does proteolytic degradation of cyclins affect the cell
cycle?: Degradation of cyclins leads to the inactivation of MPF,
allowing the cell to exit mitosis and progress to the next phase.
, 10. What is the significance of the irreversibility of cyclin
proteolysis?: Cyclin proteolysis provides an irreversible switch that
ensures the cell cycle progresses in one direction without reversal.
11. What is the checkpoint mechanism provided by proteolysis?:
Proteolysis serves as a checkpoint mechanism that ensures clean
transitions between cell cycle phases.
12. What happens in mice lacking p27?: In mice lacking p27, cells
fail to arrest properly, leading to excessive cell proliferation,
highlighting the importance of proteolytic control.
13. What is the relationship between cyclins and Cdks?: Cdks
drive progression through the cell cycle and must bind to a cyclin to
become partially active.
14. What are the two subunits that make up the Cdk-cyclin
complex?: The Cdk-cyclin complex consists of a kinase (Cdk) and a
regulator (Cyclin).
BIOD 331
BIOD 331 Module 4 Portage- Pathophysiology
Exam Questions with Correct Verified Answers
Latest Update (2025/2026) Guaranteed Pass
1. How do cyclin levels affect MPF activity?: Cyclin levels
fluctuate throughout the cell cycle; rising cyclin levels activate MPF,
pushing the cell into mitosis.
2. What is the function of the Cdk inhibitor p27?: p27 binds to
Cyclin A-Cdk2, preventing S phase progression. Its degradation allows
the cell to enter S phase.
3. What triggers the end of mitosis?: The end of mitosis is
triggered by a drop in mitotic cyclin levels, achieved through ubiquitin-
mediated proteolysis.
4. How does proteolysis ensure a clean transition between cell
cycle phases?: Proteolysis degrades cyclins to inactivate Cdks,
ensuring that the cell progresses through phases without reversal and
only when ready.
BIOD 331
,5. What is the role of phosphorylation in cell cycle regulation?:
Phosphorylation is a reversible and rapid way to regulate protein
activity, controlling the activation and inactivation of Cdks and their
regulators.
6. What is the function of Cdk-activating kinase (CAK)?: CAK
phosphorylates an activating site on the Cdk, promoting full activation
of the Cdk-cyclin complex.
7. What role does Wee1 kinase play in cell cycle regulation?:
Wee1 kinase adds a phosphate to an inhibitory site on the Cdk,
keeping it inactive even when cyclin is bound, preventing premature
entry into mitosis.
8. What is the function of Cdc25 phosphatase?: Cdc25 removes
the inhibitory phosphate added by Wee1, activating the Cdk-cyclin
complex when the cell is ready to proceed and triggering entry into
mitosis.
9. How does proteolytic degradation of cyclins affect the cell
cycle?: Degradation of cyclins leads to the inactivation of MPF,
allowing the cell to exit mitosis and progress to the next phase.
, 10. What is the significance of the irreversibility of cyclin
proteolysis?: Cyclin proteolysis provides an irreversible switch that
ensures the cell cycle progresses in one direction without reversal.
11. What is the checkpoint mechanism provided by proteolysis?:
Proteolysis serves as a checkpoint mechanism that ensures clean
transitions between cell cycle phases.
12. What happens in mice lacking p27?: In mice lacking p27, cells
fail to arrest properly, leading to excessive cell proliferation,
highlighting the importance of proteolytic control.
13. What is the relationship between cyclins and Cdks?: Cdks
drive progression through the cell cycle and must bind to a cyclin to
become partially active.
14. What are the two subunits that make up the Cdk-cyclin
complex?: The Cdk-cyclin complex consists of a kinase (Cdk) and a
regulator (Cyclin).
