4.2. Cell Division: Mitosis and Meiosis: Mitosis

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Mitosis is a form of cell division that occurs in somatic (not sex) cells and is responsible for tissue growth, development, and repair. It is a continuous process that is divided into several phases to facilitate the study.

Prophase

At the beginning of prophase, chromatin (decondensed genetic material) begins to condense into chromosomes. Each chromosome is made up of two sister chromatids, which are identical copies of the original DNA. The nucleus begins to disintegrate and the centrioles (in animal cells) move to opposite poles of the cell. Microtubules begin to form from the centrioles, initiating the formation of the mitotic spindle.

Metaphase

At metaphase, the chromosomes line up along the cell's equatorial plane, an imaginary region that is equidistant from the cell's two poles. Spindle microtubules attach to kinetochores, structures located in the centromere region of chromosomes. Each chromosome is now attached to microtubules that extend in opposite directions.

Anaphase

In anaphase, the sister chromatids separate and are pulled to opposite poles of the cell. This is facilitated by degradation of kinetochores and shortening of microtubules. At the end of anaphase, each pole of the cell has a complete set of chromosomes.

Telophase and Cytokinesis

In telophase, a new nuclear membrane begins to form around the chromosomes at each pole. The chromosomes begin to decondense back into chromatin, and the spindle microtubules begin to disassemble. Cytokinesis, the division of the cytoplasm, usually begins during anaphase or telophase. In animal cells, cytokinesis occurs through a process known as strangulation, where the ring of actin and myosin contracts around the center of the cell, forming a cleavage groove. Eventually, the groove deepens until the cell is pinched into two daughter cells, each with a nucleus containing a complete set of genes.

In short, mitosis is an intricate process that ensures that daughter cells receive an exact copy of the parent cell's genetic material. It is crucial for tissue growth, development and repair in multicellular organisms. Furthermore, mitosis is also responsible for asexual reproduction in unicellular organisms. Mistakes during mitosis can lead to genetic abnormalities and are a common cause of diseases such as cancer.

Understanding the process of mitosis is fundamental to biology, as it allows us to understand how cells divide and reproduce. This knowledge is particularly useful in medicine, as it can help us understand and treat diseases related to abnormal cell division. Therefore, mitosis is an important topic that is often covered in detail in ENEM and other similar exams.

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74.3. Cell Division: Mitosis and Meiosis: Phases of Mitosis