Lecture Notes: M Phase of the Cell Cycle

Overview

• Exploring the M phase, including mitosis and cytokinesis.
• Review of the cell cycle:
  • G1, S, G2 Phases: Make up interphase.
  • M Phase: Represents cell division.
    • Includes:
      • Mitosis: Division of the nucleus.
      • Cytokinesis: Division of the cytoplasm.

Stages of Mitosis

Mitosis is further broken down into four phases:

1. Prophase
   • Longest phase of mitosis.
   • Chromatin condenses into chromosomes.
   • Nucleolus disappears.
   • DNA coils into sister chromatids.
   • Centromere attaches sister chromatids.
   • Cytoplasm:
     • Microtubules (spindle fibers) fan out from centrioles.
     • Centrioles move to opposite sides of the cell.
   • Nuclear membrane disappears.
2. Metaphase
   • Centrioles complete movement to poles.
   • Spindle fibers align chromosomes along the equator.
   • Sister chromatids line up on either side of the equator.
3. Anaphase
   • Spindle fibers separate sister chromatids at centromere.
   • Each chromatid is now a single-stranded chromosome.
   • Chromosomes form a V-shape as they move to opposite poles.
4. Telophase
   • Nuclear membrane reforms around each set of chromosomes.
   • Chromosomes disperse into chromatin.
   • Nucleolus becomes visible again.
   • Mitosis (division of the nucleus) is complete.

Cytokinesis

• Final step of the M phase.
  • In Animal Cells:
    • Membrane moves inward, pinching cytoplasm to form two identical daughter cells.
  • In Plant Cells:
    • Cell wall material assembles along the equator, forming a cell plate.
    • Cell plate grows, joins existing membrane, and separates the two daughter cells.

Key Points to Remember

• M Phase: Fourth and final phase of the cell cycle.
  • Two processes:
    • Mitosis: Nucleus divides.
    • Cytokinesis: Cytoplasm divides.
• Mitosis Phases:
  1. Prophase: Chromatin condenses, spindle fibers form.
  2. Metaphase: Chromosomes align at the equator.
  3. Anaphase: Sister chromatids are pulled apart.
  4. Telophase: Nuclear membrane reforms, chromosomes disperse.
• Result of M Phase: Always two identical daughter cells, identical to each other and the original cell.