The basic steps of the eukaryotic cell cycle process have been known for almost half a century. The development of the molecular biological methods allowed the identification of the cell cycle regulatory genes and their products. The cycline-dependent kinases as catalytic subunits of the multiprotein nuclear enzyme complexes, regulate the cell cycle machinery in a direct way in complex with the cyclins which appear periodically and the negatively modulating cyclin inhibitors. To assure strategy of the cell for global survival during the DNA injury, the Ataxia Teleangiectasia Mutator gene function has a supervisory role in the coordination and parallel activation of the checkpoint control, p53 tumor suppressor gene, GADD45 protein and of the DNA repair, thus prevents the activation of the cell death program. The outlined regulator system gives an opportunity to explain some of the phenomena related to tumor biology and pharmacology.