The life of a eukaryotic cell can be explained as a cell cycle. Mitosis and cell division happens in the M phase that lasts for only about 1 h. This is followed by the G1 phase where G stand for gap, then the S phase S stand for synthesis, during that time the chromosomal DNA is replicated and at last the G2 phase in that the cells prepare for mitosis. Eukaryotic cells in culture classically have cell cycle times of 16-24 h but the cell cycle time can be much longer than > 100 days for some cells in a multicellular organism. Most of the variation in cell cycle times occurs by differences in the length of the G1 phase. Some cells in vivo like neurons, stop dividing totally and are said to be quiescent locked in a G0 phase.