Cell cycle

The cell cycle, or cell-division cycle, is the sequence of events that take place in a cell and lead to its division into two daughter cells. These events include the growth of the cell, duplication of its DNA (DNA replication) and some of its organelles, and subsequently the partitioning of its cytoplasm, chromosomes and other components into two daughter cells in a process called cell division. In eukaryotic cells (having a cell nucleus) including animal, plant, fungal, and protist cells, the cell cycle is divided into two main stages: interphase, and the M phase that includes mitosis and cytokinesis. During interphase, the cell grows, accumulating nutrients needed for mitosis, and replicates its DNA and some of its organelles. Its successive stages differ in their specialized biochemical processes, preparing the cell for initiation of the cell's division, but are not usually morphologically distinguishable. During the M phase, the replicated chromosomes, organelles, and cytoplasm separate into two new daughter cells. To ensure the proper replication of cellular components and division, cell cycle checkpoints follow each of the key stages of the cycle, controlling whether the cell progresses to the next. In cells without nuclei (the prokaryotes: bacteria and archaea), the cell cycle is divided into the B, C, and D periods. The B period extends from the end of cell division to the beginning of DNA replication. DNA replication occurs during the C period. The D period refers to the stage between the end of DNA replication and the splitting of the bacterial cell into two daughter cells. In single-celled organisms, a single cell-division cycle is how the organism reproduces. In multicellular organisms such as plants and animals, a series of cell-division cycles is how the organism develops from a single-celled fertilized egg into a mature organism, and is also the process by which hair, skin, blood cells, and some internal organs are regenerated and healed (with the possible exception of nerves; see nerve damage). After cell division, each of the daughter cells begins the interphase of a new cell cycle.