- Cell Cycle
The cell cycle is the well-ordered sequence of events encompassing the time a cell takes to divides into two daughter cells. The events of the cell cycle include (G1) an increase in the amount of cytoplasm and an increase in the number of organelles; (S) precise duplication of DNA; (G2) further growth of the cell and organelles; (M) mitosis, (division of the nucleus) and cytokinesis (division of the cytoplasm).

At several points in the cell cycle (checkpoints) the cell makes sure the process is occuring correctly. These cell cycle checkpoints are important in preventing mistakes in cell division.

Each daughter cell will contain a single, intact nucleus and some surrounding cytoplasm. Duration of cell cycle varies with the type of cell. Some cells divide in hours, others take more than 24 hours. Some cell types, for example, nerve and muscle cells, never or rarely divide once they mature. The stages of the Cell Cycle are: G1-S-G2-M.

Cell cycle checkpoints are regulatory pathways that control the order and timing of cell cycle transitions (e.g.G1-S) and ensure that critical events such as DNA replication and chromosome segregation are completed correctly before letting the cell progress further through the cycle. In addition, checkpoints respond to cellular damage by slowing the cell cycle to provide time for repair and by inducing transcription of genes that facilitate the repair. Checkpoint loss results in chromosomal instability (increased mutation) and can result in the transformation of normal cells into cancer cells. Recent scientific advances have revealed signal transduction pathways that transmit checkpoint signals in response to DNA damage, replication blocks, and spindle fiber damage.

Cancer a disorder of the cell cycle