Some cells, after the mitotic phase exit from the G1 phase and enter the inactive stage called quiescent stage (G0) of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism.
In the S phase of interphase, the cells duplicate their DNA. In animal cells, during the S phase, DNA replication begins in the nucleus, and the centriole duplicates in the cytoplasm.