The eukaryotic cell cycle has four key phases and an initial resting phase: G0 (resting), G1, S, G2, M. During the G1 phase a cell increase in size. It then proceeds to the S phase where DNA replication occurs. During the G2 phase, the cell continues to grow. During the M phase, cell growth stops and the cell divides into two daughter cells .

The cell cycle is controlled to ensure that everything is going properly and different points in the cycle, these points are called ‘checkpoints.’ There are checkpoints during G1, G2 and M phases which ensure that everything is ready for the subsequent phase of the cell cycle.