what happens in s phase of cell cycle

The S phase is a stage of the cell cycle that occurs during interphase, before mitosis or meiosis, and is responsible for the synthesis or replication of DNA. During this phase, the cell synthesizes a complete copy of the DNA in its nucleus. The genetic material of a cell is doubled before it enters mitosis or meiosis, allowing there to be enough DNA to be split into daughter cells. The S phase only begins when the cell has passed the G1 checkpoint and has grown enough to contain double the DNA. The S phase is halted by a protein called p16 until this happens.