Overview
This lecture covers the cell cycle in eukaryotic cells, focusing on mitosis and the mitotic index, including the stages and their significance.
The Cell Cycle
- The cell cycle includes all stages needed to create a new cell.
- Major phases: interphase (G1, S, G2), nuclear division (mitosis or meiosis), and cytokinesis (cytoplasm division).
- Interphase makes up about 90% of the cell cycle.
- G1 phase: cell grows and organelles double.
- S phase: DNA replication occurs.
- G2 phase: growth continues and DNA is checked for mutations, with faulty cells destroyed.
Mitosis: Stages and Features
- Mitosis is nuclear division producing two genetically identical, diploid cells.
- Only one round of division occurs in mitosis.
- Functions: growth, repair, and specific processes such as B cell clonal expansion in immunity.
- Stages of mitosis: Prophase, Metaphase, Anaphase, Telophase (use "PMAT" to remember order).
Stages of Mitosis
- Prophase: Chromosomes condense, become visible, centrioles move to poles, spindle fibers released, nuclear envelope disintegrates.
- Metaphase: Chromosomes align at the cell equator (metaphase plate), spindle fibers attach to centromeres and chromatids.
- Anaphase: Spindle fibers retract, centromeres divide, chromatids pulled to opposite poles; stage requires ATP.
- Telophase: Chromosomes reach poles, become longer and thinner, spindle fibers disintegrate, nuclear envelope reforms.
- Cytokinesis: Cytoplasm divides, forming two identical cells.
Mitotic Index
- The mitotic index measures the proportion of cells undergoing mitosis.
- Calculated by dividing the number of cells in mitosis by the total number of cells observed.
Key Terms & Definitions
- Eukaryotic cell — cell with a nucleus and organelles.
- Prokaryotic cell — cell lacking a nucleus (e.g., bacteria).
- Binary fission — simple cell division in prokaryotes.
- Interphase — cell cycle phase for growth, DNA replication, and preparation for division.
- Mitosis — nuclear division forming genetically identical cells.
- Cytokinesis — division of the cell’s cytoplasm.
- Chromatid — one arm of a duplicated chromosome.
- Centromere — region joining sister chromatids.
- Spindle fibers — proteins that separate chromosomes during mitosis.
- Mitotic index — ratio of cells in mitosis to total cells.
Action Items / Next Steps
- Review the stages of mitosis and be able to describe chromosome positions for each stage.
- Practice calculating the mitotic index using sample cell images.
- Prepare specific examples of mitosis applications (e.g., in immunity) for exam questions.