Overview
This lesson covers the M phase of the cell cycle, focusing on mitosis (nuclear division) and cytokinesis (cytoplasm division), and details the stages of mitosis.
The Cell Cycle and the M Phase
- The cell cycle includes interphase (G1, S, G2 phases) and the M phase (cell division).
- The M phase consists of mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).
Stages of Mitosis
- Mitosis occurs in four phases: prophase, metaphase, anaphase, and telophase.
Prophase
- Chromatin condenses into chromosomes and the nucleolus disappears.
- Replicated DNA forms sister chromatids joined at the centromere.
- Spindle fibers form from centrioles, which move to opposite poles.
- The nuclear membrane dissolves, allowing spindle fibers to attach to centromeres.
Metaphase
- Centrioles reach cell poles as spindle fibers align chromosomes along the cell’s equator.
- Sister chromatids are positioned on either side of the equator.
Anaphase
- Spindle fibers separate sister chromatids at the centromere, pulling them to opposite poles.
- Separated chromatids are now individual chromosomes.
Telophase
- Nuclear membranes reform around each chromosome set.
- Chromosomes disperse back into chromatin and the nucleolus reappears.
- Mitosis (nuclear division) ends.
Cytokinesis
- Cytokinesis divides the cytoplasm, finalizing cell division.
- In animal cells, the membrane pinches inward forming two identical daughter cells.
- In plant cells, a cell plate forms at the equator, developing into new cell walls for each daughter cell.
Key Terms & Definitions
- M Phase — stage of the cell cycle where cell division occurs.
- Mitosis — division of the cell nucleus into two identical nuclei.
- Cytokinesis — division of the cytoplasm to form two daughter cells.
- Chromatin — loose DNA and protein structure in the nucleus.
- Chromosome — condensed form of DNA visible during mitosis.
- Sister Chromatids — identical DNA copies joined at the centromere.
- Centromere — region attaching sister chromatids.
- Centrioles — paired structures organizing spindle fibers at cell poles.
- Spindle Fibers — protein structures that move chromosomes during mitosis.
- Cell Plate — structure forming in plant cells to separate daughter cells.
Action Items / Next Steps
- Review the stages of mitosis and cytokinesis.
- Compare cell division in animal vs. plant cells.
- Memorize key terms for the next class.