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Cell division


Just as a factory can be multiplied by building multiple branches, so cells divide and produce copies of themselves.

There are two types of cell division: mitosis and meiosis.

In mitosis, the division of a "mother cell" generates two genetically identical “daughter cells” with the same chromosomal number as the mother cell. An n cell produces two n cells, a 2n cell produces two 2n cells, and so on. It is an equational division.

In meiosis, the division of a “mother cell” 2n generates “daughter cells” n, genetically different. In this case, since a 2n cell produces four n cells, the division is called reductive.

Interphase - The phase that precedes mitosis

Is it impossible to imagine the multiplication of a factory, so that all branches were extremely matrixlike, with faithful copies of all components, including directors? But for most cells, this is a routine event. Mitosis corresponds to the creation of a copy of the factory and its goal is the duplication of all components.

The main activity of the cell, before dividing, refers to the duplication of its command files, that is, the reproduction of a faithful copy of the leaders in the nucleus.

Interphase is the period preceding any cell division, being of intense metabolic activity. During this period, there is the preparation for cell division, which involves the duplication of chromatin, the material responsible for controlling cell activity. All information existing throughout the DNA molecule is passed to the copy as if it were a photographic copy of the original molecule. Before long, each cell formed from the split will receive an exact copy of each chromosome of the split cell.

The two copies of each chromosome remain together for a time, joined by the common centromere, constituting two chromotids of the same chromosome. In interphase, the centrioles also duplicate.

There was a time when it was said that interphase was the period of “rest” of the cell. Today we know that interphase is in fact a period of intense metabolic activity in the cell cycle: DNA duplication, growth and synthesis. Interphase is usually divided into three distinct periods: G1, S and G2.

The time period in which DNA duplication occurs was called S (synthesis) and the preceding period is known as G1 (G1 comes from the English gap, which means "gap"). The period following S is known as G2

The whole cell cycle, including interphase (G1, S, G2) and mitosis (M) - prophase, metaphase, anaphase and telophase - can be plotted in a graph in which the amount of DNA is placed in the ordinate (y) and the time in the abscissa (x). Let's suppose that the cell to divide has, in period G1, a 2C amount of DNA (C is an arbitrary unit). The graph of DNA variation would then be similar to the one in the figure below.

In cells, there is a kind of “error checking manual” that is used in some stages of the cell cycle and is related to the checkpoints. At each checkpoint the cell evaluates whether it is possible to advance or if any adjustments are required before reaching the next phase. Often the choice is simply to cancel the process or even drive the cell to death.