Cell Cycle & Division

The ordered events by which a cell grows, duplicates its DNA, and divides

Chapter Summary

The cell cycle comprises Interphase (G₀, G₁, S, G₂) and M phase (mitosis or meiosis). Use the selector below to explore each phase’s diagram and key events. Afterwards, dive into regulation, checkpoints, and clinical relevance.


Phase diagram

G₁ (Growth)

Cell increases in size, synthesizes proteins and organelles. G₁/S checkpoint checks DNA integrity before replication.

Interphase in Depth

Interphase is when the cell prepares for division:

  • G₀: Quiescent state—cells perform normal functions (e.g., neurons).
  • G₁: Cell growth, protein/organelle synthesis, G₁/S DNA damage checkpoint.
  • S: DNA replication—each chromosome duplicates into two sister chromatids.
  • G₂: Final growth and repair, G₂/M checkpoint ensures complete replication.

Cell Cycle Regulation & Checkpoints

Progression through the cycle is tightly controlled by:

  • Cyclins & CDKs: Cyclin-dependent kinases activate phase transitions.
  • CDK inhibitors: Block kinase activity under damage/stress.
  • Tumor suppressors: p53 halts cycle if DNA damage is detected.

Key checkpoints:

  • G₁/S: checks DNA integrity before synthesis.
  • G₂/M: ensures complete replication before mitosis.
  • Spindle: verifies chromosome attachment at metaphase.

Clinical Correlations

  • Cancer: Loss of checkpoint control (e.g., mutated p53) → uncontrolled proliferation.
  • Nondisjunction: Meiosis errors → aneuploidies (e.g., Down syndrome in Meiosis I).
  • CDK Inhibitors as Drugs: Used in targeted cancer therapies to restore checkpoint control.

Key Terms

Quiz Yourself

1. Which phase includes the DNA damage checkpoint?

2. Loss of which protein often leads to cancer?

3. Nondisjunction in Meiosis I can cause which condition?