Lecture Notes: Cell Division and Mitosis

Introduction to Cell Division

• Cell division is necessary for organisms to grow, mature, and maintain tissues.
• During the mitotic phase, a cell undergoes mitosis to form two new nuclei, then divides into two individual cells in a process called cytokinesis.

Mitosis: The Process of Nuclear Division

• Mitosis is the division of duplicated DNA into two new nuclei.
• Stages of Mitosis:
  1. Prophase
     • DNA condenses and organizes, forming the classic chromosome structure.
  2. Prometaphase
     • Microtubules attach to chromosomes.
  3. Metaphase
     • Chromosomes align in the center of the cell.
  4. Anaphase
     • Chromosomes separate.
  5. Telophase
     • Nuclear membranes reappear around the two sets of chromosomes.
• Mitosis is completed once these stages are done.

Cytokinesis: Final Step of Cell Division

• Following mitosis, cytokinesis forms two new cells.
• The process involves a contractile ring compressing the cell into nearly equal halves.

The Cell Cycle

• The cell cycle involves various stages of growth and division.
• For many eukaryotic cells, the cycle repeats approximately every 24 hours.
• Interphase: Majority of a cell's life, consisting of three stages:
  • G1 (Gap 1): First growth stage; cell grows to near full size.
  • S Phase (Synthesis): DNA replication occurs.
  • G2 (Gap 2): Second growth stage; cell completes growth.

Details of Mitosis Stages

• Prophase:
  • Chromosome structure emerges through DNA condensation.
  • Microtubules appear from centrosomes; nucleolus disappears.
• Prometaphase:
  • Nuclear membrane breaks down.
  • Microtubules attach to kinetochores on sister chromatids.
• Metaphase:
  • Sister chromatids align along the cell center.
• Anaphase:
  • Sister chromatids separate due to shortening microtubules and poles moving apart.
• Telophase:
  • New nuclear membranes form; chromosomes uncoil.

Completion of Mitosis and Cytokinesis

• Post-mitosis, cytokinesis divides the cytoplasm, organelles, and other cellular components.
• Organelles divided: Mitochondria, Golgi bodies, Rough ER, and, in plant cells, chloroplasts.
• The two new cells re-enter G1 stage of interphase and begin growth and specialization.