M Phase of the Cell Cycle
Overview of the Cell Cycle
- The cell cycle consists of several phases: G1, S, G2 (interphase) and M phase.
- M phase represents cell division, which includes:
- Mitosis: Division of the nucleus
- Cytokinesis: Division of the cytoplasm
Mitosis Phases
Mitosis is divided into four key phases:
- Prophase
- Metaphase
- Anaphase
- Telophase
Prophase
- Longest phase of mitosis
- Key events:
- Chromatin condenses into chromosomes
- Nucleolus disappears
- DNA coils into sister chromatids
- Centromeres attach sister chromatids
- Spindle fibers form from centrioles (move to opposite poles)
- Nuclear membrane disappears
Metaphase
- Spindle fibers align chromosomes along the cell equator
- Sister chromatids are positioned on either side of the equator
Anaphase
- Spindle fibers separate sister chromatids at centromeres
- Chromatids become individual chromosomes
- Chromosomes move to opposite poles, forming a V-shape
Telophase
- Nuclear membrane reforms around each set of chromosomes
- Chromosomes spread out into chromatin
- Nucleolus reappears
- Mitosis is complete
Cytokinesis
-
Final step of M phase
-
In Animal Cells:
- Cell membrane pinches inward, creating two identical daughter cells
-
In Plant Cells:
- Cell wall material assembles along the equator to form a cell plate
- Cell plate grows and fuses with the existing cell membrane, separating daughter cells
- New cell walls form between daughter cells over time
Key Points to Remember
- The M phase is the fourth and final phase of the cell cycle.
- It includes two processes: mitosis (nucleus divides) and cytokinesis (cytoplasm divides).
- Mitosis consists of four phases:
- Prophase: Chromatin condenses; spindle fibers form.
- Metaphase: Chromosomes align at the equator.
- Anaphase: Sister chromatids are separated to opposite poles.
- Telophase: Nucleolus and nuclear membrane reform; chromosomes disperse.
- Cytokinesis finalizes division of the cytoplasm.
- Result: Two identical daughter cells.