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## Mitosis Mitosis is the division of the nucleus of a cell. At the end of this stage, each daughter cell receives a set of chromosomes. To achieve this, the duplication of the chromosomes is required. ### 1.1 Prophase This phase comprises approximately 80% of the total duration of cell divisi...

## Mitosis Mitosis is the division of the nucleus of a cell. At the end of this stage, each daughter cell receives a set of chromosomes. To achieve this, the duplication of the chromosomes is required. ### 1.1 Prophase This phase comprises approximately 80% of the total duration of cell division. It is therefore the longest stage in the cell cycle. During prophase, we can observe the following phenomena that occur progressively: * In the cytoplasm, the cytoskeleton is dismantled to create a new cytoskeleton, which is necessary for the microtubules to intervene in mitosis. Therefore, the cytoplasm becomes more viscous. * Within the nucleus, chromosomes condense and become visible as structured filaments. They also disperse the nucleolus material. * The nuclear envelope fragments forming membranes similar to the endoplasmic reticulum. At the end of the process, the chromosomes come into contact with the cytoplasm. * Each sister chromatid (represented by a chromosome) has a protein ring called the kinetochore, which is linked to the microtubules of the mitotic spindle. Each of the two copies obtained after the duplication of a chromosome is called a chromatid. Since both come from the same chromosome, we often call them sister chromatids. During the early stages of mitosis, sister chromatids remain bound by the centromere. ### 1.2 Metaphase * The centrioles are separated and move to the poles of the cell. As they move apart, microtubule groups form between them, forming the spindle fibers. * **Kinetochore fibers**: Microtubules of the spindle linked to the kinetochores. * **Polar fibers**: Microtubules of the spindle not linked to the kinetochores. * **Astral fibers**: Outer microtubules of the spindle. * The chromosomes align on the equator of the cell. * The spindle fibers connect to the centromere of each chromosome, holding them in position on the metaphase plate. In cells that don't possess centrioles, such as plants, spindle fibers are directed by the plasma membrane and the poles of the cell.