Difficulty: Easy
Correct Answer: regulate passage from one stage of cell division to another
Explanation:
Introduction / Context:
Cyclins are central timers of the eukaryotic cell cycle. Their periodic accumulation and degradation drive orderly transitions through G1, S, G2, and M phases by activating cyclin-dependent kinases (CDKs).
Given Data / Assumptions:
Concept / Approach:
Cyclins do not act alone; they form complexes with CDKs. These complexes phosphorylate target proteins that promote DNA replication, mitotic entry, and mitotic progression. Cyclin levels are tightly regulated by synthesis and proteasomal degradation to ensure one-way progression.
Step-by-Step Solution:
Recognize cyclin hallmark: oscillating expression patterns.Link function: activate CDKs to trigger phase transitions.Therefore, cyclins regulate passage between cell cycle stages.
Verification / Alternative check:
Loss- or gain-of-function of cyclins alters timing of S-phase entry or mitosis; cyclin destruction boxes control exit from mitosis.
Why Other Options Are Wrong:
Common Pitfalls:
Equating cyclins with constant “on” signals; in reality, their cyclical degradation is essential for directionality.
Final Answer:
regulate passage from one stage of cell division to another
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