In eukaryotic cells, which phases together constitute the full cell cycle framework within which DNA replication occurs?
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AG1, G2 and M only
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BS, G2 and M only
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CG1, S, G2 and M
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DG2 and M only
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ES phase only (no other phases)
Answer
Correct Answer: G1, S, G2 and M
Explanation
Introduction / Context:DNA replication is restricted to a defined window of the eukaryotic cell cycle, but understanding that window requires viewing the entire cycle framework that orchestrates growth, synthesis, checkpoint control, and division.
Given Data / Assumptions:
- Interphase consists of G1, S, and G2.
- M phase encompasses mitosis and cytokinesis.
- DNA replication itself occurs during S phase.
Concept / Approach:The complete canonical eukaryotic cell cycle is G1 (growth), S (DNA synthesis), G2 (preparation/checking), and M (mitosis). Many exam items ask for the set of phases constituting the cycle, not only the single phase where replication happens.
Step-by-Step Solution:
List all standard phases: G1, S, G2, M.Identify replication window: S phase.Select the option that includes the full framework (not a subset): G1, S, G2 and M.Confirm that other options omit necessary phases.Verification / Alternative check:Cell-cycle markers (cyclins/CDKs) and DNA content analysis (flow cytometry) define these stages, with 1C → 2C DNA increase in S phase.
Why Other Options Are Wrong:
- G1, G2 and M: omits S phase.
- S, G2 and M: omits G1.
- G2 and M: incomplete.
- S only: names the synthesis phase, not the whole cycle.
Common Pitfalls:Answering “S phase” when the question asks for the cell-cycle composition rather than the replication window.
Final Answer:G1, S, G2 and M