Figure 3.

Cell cycle checkpoints inducing cell cycle arrest. Three points in the cell cycle are usually determined for normal cell growth. At the G1 cell checkpoint, when DNA damage is observed, the cell automatically turns to the G0 state (resting state), thus stopping the cell from growing any further. At the G2 cell checkpoint, the cell size is observed and the DNA replication is examined. When either of these processes is not yet complete or erroneous, cell cycle arrest is induced. At the spindle assembly checkpoint, whether the chromosomes are attached to the spindle is examined.