Lecture Notes: Mitosis and Cell Division

Overview

• Interphase: Bulk of cell's life cycle; involves growth and DNA replication.
• Mitosis: Process where one nucleus divides into two nuclei with identical genetic information.
• Cytokinesis: Splitting of the cytoplasm, resulting in two separate cells.

Phases of Mitosis

1. Prophase

• DNA Condensation: Chromosomes transition from chromatin form to condensed form, visible under a microscope.
  • Each chromosome consists of two sister chromatids connected at the centromere.
• Nuclear Membrane Disintegration: Starts to disappear.
• Centrosomes Migration: Move to opposite sides of the cell.
• Chemical and Thermodynamic Reactions: Coordinate these processes without cellular intelligence.

2. Metaphase

• Nuclear Membrane Gone: Allows chromosomes to line up at the cell's equator.
• Centrosomes at Opposite Ends: Connected by microtubules.
• Microtubules Role: Extend from centrosomes to centromeres, aiding in alignment and future chromatid separation.
• Centrioles: Cylindrical structures within centrosomes.

3. Anaphase

• Microtubules Pulling: Sister chromatids are separated and pulled towards opposite centrosomes.
  • Chromatids become individual chromosomes upon separation.
• Kinetochore: Site where microtubules connect to chromosomes.

4. Telophase

• Reformation of Nuclear Membranes: Around the separated DNA.
• Chromosome De-condensation: Transition back to chromatin form.
• Cell Membrane Pinching: Prepares for cytokinesis by beginning to divide the cell into two.

Cytokinesis

• Process: Final cell division, completes separation into two cells.
• Timing: Begins in anaphase and continues through telophase.
• Result: Two separate cells each entering interphase and capable of future division.

Additional Notes

• Terminology: Centrosomes, centromeres, centrioles, microtubules, and kinetochores are critical terms.
• Unresolved Questions: Some molecular mechanisms of cell division remain under research.
• Cycle Continuation: Post-cytokinesis, cells enter interphase, preparing for potential future division.