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Jai Ganesh

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Registered: 2005-06-28

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Mitosis

Mitosis

Gist

Mitosis is the process of cell division where a parent cell duplicates its chromosomes and divides to form two genetically identical daughter cells. It involves five main phases—prophase, prometaphase, metaphase, anaphase, and telophase—and is crucial for growth, repair, and asexual reproduction. This process ensures that each new cell receives the same number of chromosomes as the original cell.

Mitosis is important for growth, repair, and reproduction, as it creates genetically identical cells. It is the process by which organisms grow from a single cell into a multicellular being, replaces old or damaged cells (like skin cells), and allows single-celled organisms to reproduce asexually. This ensures that new cells have the exact same genetic information as the parent cell, which is crucial for maintaining the integrity of tissues and the organism as a whole.

Summary

Mitosis is a part of the cell cycle in eukaryotic cells in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis is an equational division which gives rise to genetically identical cells in which the total number of chromosomes is maintained. Mitosis is preceded by the S phase of interphase (during which DNA replication occurs) and is followed by telophase and cytokinesis, which divide the cytoplasm, organelles, and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components. This process ensures that each daughter cell receives an identical set of chromosomes, maintaining genetic stability across cell generations. The different stages of mitosis altogether define the mitotic phase (M phase) of a cell cycle—the division of the mother cell into two daughter cells genetically identical to each other.

The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are preprophase (specific to plant cells), prophase, prometaphase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have already duplicated during interphase, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell. The result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells. The different phases of mitosis can be visualized in real time, using live cell imaging.

An error in mitosis can result in the production of three or more daughter cells instead of the normal two. This is called tripolar mitosis and multipolar mitosis, respectively. These errors can be the cause of non-viable embryos that fail to implant. Other errors during mitosis can induce mitotic catastrophe, apoptosis (programmed cell death) or cause mutations. Certain types of cancers can arise from such mutations.

Mitosis varies between organisms. For example, animal cells generally undergo an open mitosis, where the nuclear envelope breaks down before the chromosomes separate, whereas fungal cells generally undergo a closed mitosis, where chromosomes divide within an intact cell nucleus. Most animal cells undergo a shape change, known as mitotic cell rounding, to adopt a near spherical morphology at the start of mitosis. Most human cells are produced by mitotic cell division. Important exceptions include the gametes – sperm and egg cells – which are produced by meiosis. Prokaryotes, bacteria and archaea which lack a true nucleus, divide by a different process called binary fission.

Details

Mitosis is a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells. Strictly applied, the term mitosis is used to describe the duplication and distribution of chromosomes, the structures that carry the genetic information.

A brief treatment of mitosis follows.

Prior to the onset of mitosis, the chromosomes have replicated and the proteins that will form the mitotic spindle have been synthesized. Mitosis begins at prophase with the thickening and coiling of the chromosomes. The nucleolus, a rounded structure, shrinks and disappears. The end of prophase is marked by the beginning of the organization of a group of fibres to form a spindle and the disintegration of the nuclear membrane.

The chromosomes, each of which is a double structure consisting of duplicate chromatids, line up along the midline of the cell at metaphase. In anaphase each chromatid pair separates into two identical chromosomes that are pulled to opposite ends of the cell by the spindle fibres. During telophase, the chromosomes begin to decondense, the spindle breaks down, and the nuclear membranes and nucleoli re-form. The cytoplasm of the mother cell divides to form two daughter cells, each containing the same number and kind of chromosomes as the mother cell. The stage, or phase, after the completion of mitosis is called interphase.

Mitosis is absolutely essential to life because it provides new cells for growth and for replacement of worn-out cells. Mitosis may take minutes or hours, depending upon the kind of cells and species of organisms. It is influenced by time of day, temperature, and chemicals.

Additional Information

Mitosis is the process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division. Mitosis is generally followed by equal division of the cell’s content into two daughter cells that have identical genomes.

We can think about mitosis like making a copy of an instruction manual. Copy each page, then give one copy to each of two people. In mitosis, a cell copies each chromosome, then gives one copy to each of two daughter cells. With our instruction manual example, it is really important that each person gets one copy of every page. We don't want to accidentally give one person two copies of page four and one person zero copies of page four. And the copies need to be perfect. No misspellings, no deletions. Otherwise, we might not be able to follow the instructions and things could go wrong. This is also true with mitosis. We need each of our cells to receive exactly one copy of each chromosome, and each copy needs to be perfect, no mistakes, or the cells may have trouble following the genetic instructions. Fortunately, our cells have amazing systems to copy chromosomes almost perfectly and to make sure that one copy goes to each daughter cell. Still, very rarely mistakes in copying or dividing chromosomes are made, and these mistakes can have negative consequences for cells and for people.

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