The g1 phase of interphase is the first of 3 steps interphase of the cell cycle, in this phase it takes place in the eukaryotic cell division, the cell synthesizes mRNA and proteins in preparation for steps leading to mitosis. g1 phase ends when the cells moved into the S phase of interphase.
The S phase happens when the cell has reached an appropriate size and is in a supportive environment for DNA replication, it will exit g1 phase and enter the next phase of interphase called S phase. S phase, or synthesis, is the phase of the cell cycle when DNA packaged into chromosomes is replicated.
After DNA replication, the cell leaves S phase and enters G2, when the cell prepares for mitosis or meiosis. At the G2 checkpoint, the cell checks two things. First, it checks DNA for any damage that might have occurred during replication. It also ensures all the proteins needed for cell division are present