The cell cycle

Cell, prokaryotic or eukaryotic, reproduce to give rise to new daughter cells which, after growing and fulfilling their functions, will reproduce again to give rise to new cells.

The cell cycle is the sequence of events that take place from the time a cell originates by division of a previous cell, until it divides again to give rise to new daughter cells.

Although almost all cells can divide, there are some exceptions. Muscle cells or neurons cannot divide. Others, such as those of the intestinal epithelium, usually take about 8 hours to divide.

For many single-celled organisms, the cell cycle constitutes their life cycle and the birth of a new organism.

For multicellular organisms, the cell cycle of their cells allows their growth and the repair of damaged tissues.

In eukaryotic cells, the cell cycle is divided into two stages:

• Interphase.

• Cell division or M phase (mitosis).

Cell division or M phase (mitosis)

The division phase or M phase is the final, shorter stage, in which a cell will have a mitotic division whereby it will originate two cells with the same amount of DNA as the cell that originated them.

The cell division phase or M phase has two stages:

• Karyokinesis or division of the nucleus (mitosis).
• Cytokinesis or division of the cytoplasm. Very short stage that only lasts 10% of the cell cycle, approximately.

In unicellular beings, cell reproduction coincides with the formation of a new individual.

In multicellular beings, cell reproduction serves so that the organism can grow and replace the cells that have been dying. In multicellular cells, all cells reproduce by mitosis, except for reproductive cells or gametes (ovules and sperm), which reproduce by meiosis.

Remember that when the cell is dividing, the two identical chromatin (DNA) chains spiral into chromosomes. The number of chromosomes in the human species is 2n = 46, forming 23 pairs of chromosomes.