Introduction
Mitosis is a type of cell division in which a single parent cell divides to form two genetically identical daughter cells. It is a fundamental process for growth, development, tissue repair, and asexual reproduction in multicellular organisms. Mitosis occurs in somatic (body) cells and maintains the chromosome number (diploid, 2n) of the parent cell in the daughter cells.
Definition of Mitosis
Mitosis is defined as the division of the nucleus and its chromosomes into two identical nuclei, followed by the division of the cytoplasm (cytokinesis), resulting in two daughter cells with the same number of chromosomes as the original cell.
Phases of Mitosis
Mitosis is a continuous process but is divided into five distinct stages for understanding purposes:
1. Prophase
- Chromatin (loose DNA) condenses to form visible chromosomes.
- Each chromosome consists of two sister chromatids joined at a centromere.
- The nuclear membrane begins to break down.
- Spindle fibers start to form from the centrosomes.
2. Prometaphase
- The nuclear envelope completely disintegrates.
- Spindle fibers attach to the kinetochores (protein structures) of chromosomes.
3. Metaphase
- Chromosomes align at the center of the cell, called the metaphase plate.
- This alignment ensures that each daughter cell will receive one copy of each chromosome.
4. Anaphase
- Sister chromatids are pulled apart by spindle fibers towards opposite poles of the cell.
- This ensures each pole gets an identical set of chromosomes.
5. Telophase
- Chromosomes begin to de-condense into chromatin.
- Nuclear envelopes reform around each set of chromosomes.
- Spindle fibers disintegrate.
Cytokinesis
Although not a part of mitosis, cytokinesis usually follows telophase. It involves the division of the cytoplasm to form two separate daughter cells.
- In animal cells: A cleavage furrow forms to pinch the cell in two.
- In plant cells: A cell plate forms, eventually developing into a new cell wall.
Diagrams of Mitosis Stages
Below is a simple illustration (please refer to your textbook for detailed labeled diagrams):
- Prophase: Chromosomes condense, spindle forms
- Metaphase: Chromosomes line up at the center
- Anaphase: Sister chromatids separate
- Telophase: Two nuclei form
- Cytokinesis: Cell splits into two
Importance of Mitosis
- Maintains genetic stability across generations of cells
- Essential for growth and development of organisms
- Helps in tissue repair and regeneration
- Enables asexual reproduction in some organisms
Conclusion
Mitosis is a vital process that ensures the continuity of life by producing identical cells for various functions in the body. Each stage of mitosis is carefully regulated to maintain genetic accuracy. Understanding mitosis helps in the study of genetics, cancer research, and cellular biology.