Figure 1.

Schematic presentation of the eukaryotic cell cycle and its regulation. The eukaryotic cell cycle consists of two gap phases, the G1 and the G2 phase, the S-phase, and the M (mitosis) phase. Cells can also enter a quiescent state, the G0 phase. Cell cycle phases are indicated by colored arrows. The cell cycle is regulated by complexes that are composed of cyclins, which are bound to cyclin-dependent protein kinases (CDKs). Cyclin-CDK complexes are positioned in the front of the arrow that designates the corresponding cell cycle phase. Cyclin-CDK complexes are controlled via checkpoint pathways whose role is to prevent the cell from progressing to the next stage when it is not allowed. Multiple stimuli that exert the checkpoint control are indicated in an appropriate text insert.