4.1. Cell Division: Mitosis and Meiosis: Cell Cycle

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4.1. Cell Division: Mitosis and Meiosis: Cell Cycle

Cell division is a fundamental process for life. It is responsible for the growth, development and regeneration of organisms. There are two types of cell division: mitosis and meiosis. Both are integral parts of the cell cycle, which is the process a cell goes through from its formation to its own division into two daughter cells.

Mitosis

Mitosis is a type of cell division that results in two daughter cells that are genetically identical to the parent cell. It is the process by which the body grows and replaces cells that have died or been damaged. Mitosis is a continuous process that is divided into four main phases: prophase, metaphase, anaphase, and telophase.

Prophase

In prophase, the first phase of mitosis, the cell nucleus disappears and the chromosomes begin to condense. Each chromosome is made up of two sister chromatids, which are identical copies of the same DNA. The centriole, a cellular structure, begins to move to the opposite poles of the cell.

Metaphase

At metaphase, the chromosomes line up at the cell's equator, a stage known as the metaphase plate. Spindle fibers, originating from centrioles, attach to the centromeres of chromosomes.

Anaphase

In anaphase, the sister chromatids separate and move to opposite poles of the cell. This movement is facilitated by the spindle fibers.

Telophase

In telophase, the chromosomes begin to decondense and two nuclei are formed, each containing a complete set of chromosomes. The cell then divides into two, a process called cytokinesis.

Meiosis

Meiosis is a type of cell division that results in four daughter cells, each with half the number of chromosomes as the parent cell. Meiosis is the process by which gametes, or sex cells, are produced. Meiosis is also divided into several phases, but it occurs in two rounds of cell division: meiosis I and meiosis II.

Meiosis I

In meiosis I, homologous chromosomes pair up and exchange genetic material in a process called crossing over. This is followed by the separation of homologous chromosomes. At the end of meiosis I, there are two daughter cells, each with half the number of chromosomes as the mother cell.

Meiosis II

In meiosis II, the sister chromatids separate, just like in anaphase of mitosis. At the end of meiosis II, there are four daughter cells, each with half the number of chromosomes as the parent cell. These daughter cells are the gametes.

In summary, mitosis and meiosis are cell division processes that play vital roles in the growth, development, and reproduction of organisms. Understanding these processes is fundamental to understanding biology at a cellular and molecular level, and is a key topic for the ENEM exam.

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64.2. Cell Division: Mitosis and Meiosis: Mitosis