Explain how the cell cycle is normally controlled, including reference to the role of tumor-suppressor genes:

The cell cycle is composed of S (synthetic) phase and M (Mitotic) phase. In between are G1 and G2 phases. cyclin-dependent kinases propel cell division. Their activation results in the progression of a cell from one phase to another while their inactivation arrests a cell in a phase. In case of damage to DNA during a cell cycle, transcription factors p53 (a renowned tumor suppressor) are recruited. P53 inhibits cyclins-dependent kinases and also induces cell apoptosis if DNA is not repaired.