Mitosis Lecture Notes

Introduction to Mitosis

• Cell Cycle: Involves cells copying the genome and growing for cell division.
• Mitosis: The process of cell division; results in two identical cells with complete genetic information.

Phases of Mitosis

1. Prophase

   • Chromatin coils to form chromosomes with sister chromatids linked by a centromere.
   • The mitotic spindle forms, composed of centrosomes and microtubules.
   • Centrosomes have a radial array of microtubules called an aster.
   • Microtubules grow and push centrosomes apart.

2. Prometaphase

   • The nucleus breaks apart.
   • Microtubules cover the former nuclear area to attach to kinetochores on chromosomes.
   • Kinetochores assemble at centromeres.

3. Metaphase

   • Centrosomes are at the cell poles.
   • Chromosomes align along the metaphase plate.
   • Checkpoint ensures sister chromatids are attached to opposite spindle ends.
   • Activation of a regulatory protein complex allows progression to anaphase.

4. Anaphase

   • The enzyme separase cleaves cohesins between sister chromatids.
   • Kinetochores pull chromatids apart.
   • Motor proteins move chromosomes to opposite cell ends.
   • Cell elongates.

5. Telophase

   • Two new nuclei form.
   • Chromosomes loosen.
   • Microtubules disassemble.

Cytokinesis

• Cytoplasm divides, forming two distinct cells.
• Cleavage furrow forms at the metaphase plate.
• Actin microfilaments pull the cell like a drawstring, pinching it into two.

Importance of Mitosis

• Produces new cells for growth, skin renewal, and healing.
• All somatic cells, except the initial fertilized egg, are a result of mitosis.

Outlook

• Next topic will explore the production of reproductive cells (gametes), which occurs through a different process from mitosis.