When Is DNA Replicated During the Cell Cycle?

DNA is replicated during interphase, the phase of the cell cycle that precedes the four stages of mitosis: anaphase, prophase, prometaphase and telophase. According to CyberBridge, a life sciences website maintained by Harvard University, DNA replication occurs during the S phase of interphase.

Cells spend 90 percent of their time in interphase, during which the cell grows, produces proteins, replicates DNA and prepares for mitosis. As with the remainder of the cell cycle, these processes occur in stages, not all at once. Interphase is divided into three main stages: G1, S and G2. During the S phase of interphase, which follows G1, all of the chromosomes are replicated. After replication, each cell now consists of two sister chromatids.

Although the actual amount of DNA doubles, its ploidy, the chromosome count, remains the same. Human cells remain diploid after replication, which means they maintain a count of 46 chromosomes. In other words, the number of chromatids doubles during replication. However, the number of chromosomes and centromeres remains unchanged.

After replication, interphase continues into its G2 phase, which synthesizes proteins. The cell then into the remainder of the cell cycle or into G0. According to CyberBridge, G0 is a stage of interphase for non-replicating cells in which the cells remain dormant until new cells are needed.