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Topic Notes · Easy summaries with diagrams
Chapter 4 — Chapter 4 — Cell Cycle
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📘Easy summary
The cell cycle is the series of events that take place in a eukaryotic cell from its formation to its division into two daughter cells. It has two main phases: interphase and the mitosis (M) phase.
Interphase lasts about 90% of the cell cycle; the cell performs its life functions and prepares for the next division.
⭐Key points
- G1 (first gap / growth phase): cell makes proteins and organelles and grows; makes enzymes for DNA replication.
- S (synthesis) phase: DNA of each chromosome is replicated; each chromosome has two sister chromatids; chromosome number stays the same.
- G2 (second gap): cell grows, makes proteins for division, checks and repairs DNA damage.
- G0 phase: cells stop dividing — neurons stay indefinitely; liver and kidney cells temporarily; epithelial cells never enter G0.
- Events of the cell cycle are controlled by special genes.
🔬Diagram
🌿Real-life example
Skin cells keep cycling all life to replace worn skin, while nerve cells sit in G0 and do not divide.
💡Exam tip
- Maximum growth = G1 (MCQ 1); chromosomes duplicate in S (MCQ 2).
- Interphase ≈ 90% of the cycle.
✅Quick check
1. DNA replication occurs in:
2. Neurons remain in which phase for indefinite periods?
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