Cell cycle

• Cell cycle

  Highly organised process behind cell division and other phenomena
• Cell division

  • Most cell division results in 2 daughter cells with identical genetic information, DNA - mitosis
  • Cell division linked to reproduction is called meiosis
• Cell division is important for:
• Post-mitotic cells

  Cells that never divide
• Senescent cells


  Cells that lose the ability to divide during ageing
• Speed of the cell cycle varies depending on cell type
• Typical cell cycle durations

  • Eukaryote cell = 24 hr
  • Hepatocyte (liver cell) = 1-2 years
  • Neurones, heart cells = never
  • Bacteria = 20 minutes
• G1 phase

  Growth phase, cell undergoes protein synthesis, gene transcription, RNA synthesis, organelle duplication
• S phase

  DNA duplication, chromosome duplication and condensation
• G2 phase

  Cell growth, DNA check for errors
• M phase

  Nuclear envelope breakdown, mitotic spindle formation, chromosome separation, cytokinesis
• Prophase

  Chromatin condenses into chromosomes, nucleolus disappears, nuclear envelope starts to break down, microtubule activity increases
• Prometaphase


  Nuclear envelope continues to break down, microtubules attach to kinetochores, chromosomes move to centre
• Metaphase

  Chromosomes align at metaphase plate
• Kinetochore

  Structure that attaches chromosomes to microtubules, leading to chromosome segregation
• Anaphase

  Sister chromatids separate, kinetochore microtubules shorten to draw chromatids to opposite poles
• Telophase


  Chromosomes reach opposite ends, nuclear envelope reforms, nucleolus reforms, cytokinesis begins
• Cytokinesis in animal cells

  Cleavage furrow forms, contractile ring of microfilaments divides cell
• Cytokinesis in plant cells

  Cell plate forms between daughter cells, new cell wall develops
• Bacterial cell division involves chromosome replication and separation into two daughter cells
• Cell cycle checkpoints monitor the cell cycle and can halt progression if problems are detected
• Further reading: Biology: How Life Works, Chapter 11; Alberts et al "Molecular Biology of the Cell", Chapter 17
• Cell cycle order


  1. G1- growth, interphase

  2. S- DNA synthesis, interphase

  3. G2- growth and preparation for mitosis, interphase

  4. M- mitosis, PMAT then C