Expand G1S and G2M

The S phase of a cell cycle occurs during interphase, before mitosis or meiosis, and is responsible for the synthesis or replication of DNA. In this way, 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. Between G1 and S phase, three DNA damage checkpoints occur to ensure proper growth and synthesis of DNA prior to cell division. Damaged DNA during G1, before entry into S phase, and during S phase result in the expression of ATM/R protein. Interphase is divided into the first growth (G1), Synthesis (S), and the second growth (G2) phases (figure 1). The growth phases are, as you may have suspected, for the growth of the cell, during the synthesis phase the DNA replication occurs in preparation for the second growth phase.