Overview
This lecture covers the process of mitosis, the phases involved, the structures responsible for chromosome movement, and the outcome of cell division.
The Cell Cycle and Preparation for Mitosis
- The cell cycle includes genome duplication and cell growth in preparation for cell division.
- In the G2 phase, chromosomes are duplicated and centrosomes have two pairs of centrioles.
Phases of Mitosis
- Mitosis consists of five phases: prophase, prometaphase, metaphase, anaphase, and telophase.
- Prophase: Chromatin condenses into chromosomes; sister chromatids join at the centromere; mitotic spindle (made of centrosomes and microtubules) starts to form; asters appear.
- Prometaphase: Nuclear envelope breaks apart; microtubules attach to kinetochores on chromosomes.
- Metaphase: Centrosomes at cell poles; chromosomes align along the metaphase plate; metaphase checkpoint ensures proper attachment.
- Anaphase: Separase enzyme cleaves cohesins; sister chromatids are pulled apart to opposite poles by motor proteins; cell elongates.
- Telophase: New nuclear envelopes form around chromosomes; chromosomes de-condense; spindle breaks down; two identical nuclei result.
Cytokinesis
- Cytokinesis divides the cytoplasm, forming two separate cells via a cleavage furrow created by actin microfilaments.
Outcome of Mitosis
- Mitosis produces two genetically identical somatic cells, each with the organism’s complete genetic information.
- All somatic cells except the first fertilized egg are formed through mitosis; reproductive cells (gametes) are formed by a different process.
Key Terms & Definitions
- Mitosis — process of dividing a cell’s nucleus to create two identical nuclei.
- Centrosome — organelle containing two centrioles, organizing microtubules.
- Chromatid — one half of a duplicated chromosome.
- Centromere — region joining two sister chromatids.
- Mitotic spindle — structure made of centrosomes and microtubules that segregates chromosomes.
- Aster — radial array of microtubules around each centrosome.
- Kinetochore — protein complex on the centromere where spindle fibers attach.
- Metaphase plate — imaginary plane where chromosomes align during metaphase.
- Separase — enzyme that cleaves cohesins to separate sister chromatids.
- Cytokinesis — division of the cytoplasm resulting in two distinct cells.
- Cleavage furrow — indentation that begins the process of cytokinesis.
Action Items / Next Steps
- Review the five phases of mitosis and their key events.
- Prepare to learn about meiosis, the process that produces gametes.