The cell cycle of mitosis describes the process of cell division, specifically focusing on the duplication of a cell's nucleus and its chromosomes. It’s a fundamental process for growth, repair, and asexual reproduction in many organisms.
Phases of the Mitotic Cell Cycle
Mitosis is conventionally divided into distinct phases that ensure the accurate distribution of genetic material. These phases, along with the preparatory interphase, constitute the complete mitotic cell cycle.
Interphase (Pre-Mitosis)
- This is not technically part of mitosis but is the preparatory phase before cell division.
- Nuclear Envelope: A nuclear envelope surrounds the nucleus.
- DNA Replication: DNA is replicated during the S phase of interphase, resulting in two identical copies of each chromosome.
- Sister Chromatids: These identical copies, called sister chromatids, join together at the centromere.
- Interphase includes G1, S, and G2 phases; the S phase is particularly significant as this is where DNA replication happens.
Mitosis Proper
The process of mitosis itself is broken down into four distinct stages:
- Prophase:
- Chromosomes condense and become visible.
- The nuclear envelope starts to break down.
- The mitotic spindle begins to form.
- Metaphase:
- Chromosomes align at the cell's equator (metaphase plate).
- Each sister chromatid is attached to a spindle fiber originating from opposite poles.
- Anaphase:
- Sister chromatids separate at the centromere, and each is now considered a full chromosome.
- The newly separated chromosomes are pulled to opposite poles of the cell by the spindle fibers.
- Telophase:
- Chromosomes arrive at the poles and begin to decondense.
- The nuclear envelope reforms around each set of chromosomes.
- Two new nuclei are formed.
Cytokinesis (Post-Mitosis)
- Cell Division: This is the final step where the cytoplasm divides, resulting in two separate, genetically identical daughter cells.
Summary
| Phase | Description |
|---|---|
| Interphase | DNA replication, cell growth, preparation for mitosis; chromosomes joined at centromere. |
| Prophase | Chromosomes condense, nuclear envelope breaks down, spindle forms. |
| Metaphase | Chromosomes align at the equator. |
| Anaphase | Sister chromatids separate and move to opposite poles. |
| Telophase | Chromosomes decondense, new nuclei form, nuclear envelope reforms. |
| Cytokinesis | Cell cytoplasm divides to create two daughter cells. |
The mitotic cell cycle is crucial for the proper growth and maintenance of tissues, ensuring that each new cell has the complete and correct genetic material.
