Cell Biology
Mitosis
One cell becomes two identical daughters
Mitosis is the process of cell division where a single somatic cell replicates its DNA and divides into two genetically identical daughter cells, a cycle that takes approximately 24 hours in human tissues. While the entire M-phase lasts only about an hour, it is a masterclass in biological precision, using a mitotic spindle to pull sister chromatids apart at a speed of 1 micrometer per second. With approximately 37 trillion cells in the human body, mitosis is the essential engine of growth, tissue repair, and the constant renewal of life.
- Cell Cycle~24 hours (Somatic)
- M-Phase~1 hour duration
- Pull Speed1 μm per second
- Total Cells~37 Trillion per human
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How it works
Mitosis is divided into four main stages. In Prophase, the DNA condenses into visible chromosomes. In Metaphase, the chromosomes line up in the center of the cell. In Anaphase, the 'mitotic spindle' (protein cables) pulls the sister chromatids apart toward opposite ends. Finally, in Telophase, two new nuclei form and the cell pinches in two (cytokinesis). The result is two cells with the exact same genetic blueprint.
Precision and Cancer
The body has strict 'checkpoints' to ensure mitosis happens correctly. If the chromosomes aren't lined up perfectly in metaphase, the cell will pause or even self-destruct (apoptosis). When these checkpoints fail and mitosis becomes uncontrolled, cells divide every 24–48 hours without stopping, leading to the formation of a tumor. Chemotherapy often works by targeting and breaking the mitotic spindle to stop this runaway growth.
Common pitfalls
- Confusing with Meiosis: Mitosis creates identical somatic cells (46 chromosomes); Meiosis creates unique sex cells (23 chromosomes).
- Ignoring Interphase: Mitosis is only the 'division' part. Most of a cell's life is spent in Interphase, where it grows and copies its DNA in preparation for the split.
- Thinking it's 'Fast': While 1 hour sounds quick, pulling a chromosome 10 micrometers at 1 μm/sec is a massive mechanical feat for a microscopic structure.
| Feature | Mitosis | Meiosis |
|---|---|---|
| Purpose | Growth, Repair, Asexual reproduction | Sexual reproduction (Gametes) |
| Daughter Cells | Two identical cells | Four unique cells |
| Chromosome Count | Diploid (46 in humans) | Haploid (23 in humans) |
| Genetic Variation | None (Clones) | High (Crossing over) |
Frequently asked questions
What is a chromatid?
One half of a replicated chromosome. Before they are pulled apart in anaphase, two identical 'sister' chromatids are joined at the center.
Why do cells need to divide?
To replace old or damaged cells (like skin cells), to allow an organism to grow, and to keep the cell size small enough for efficient nutrient transport.
What is the spindle made of?
Microtubules—strong protein fibers that act as both the 'cables' and the 'motors' that move chromosomes.
Do all cells undergo mitosis?
Most do, but some highly specialized cells, like mature neurons or red blood cells, rarely or never divide once they are fully formed.
What happens if mitosis goes wrong?
It can lead to 'Aneuploidy' (wrong number of chromosomes), which is a hallmark of cancer and certain genetic disorders.