The cell cycle refers to the distinct stages through which a cell goes, from the moment it becomes a cell to the moment it divides to result in 2 separate cells. Bear in mind that some cells cease to divide any longer after a certain period of time, depending on cell type. If that’s the case, they are said to be in resting phase termed G0.
Within the dividing cell, it starts with gap 1, G1, continues into the S phase (S is for Synthesis) where DNA replicates, followed by gap 2, G2, and ending with mitosis.
G1 and G2 may sound like codes for some complex enzymes, but they are mere notations for gaps 1 and 2, which are just that: gaps between mitosis and DNA replication (in the S phase) respectively. G1 through to G2 – that’s G1, S phase and G2 – are all stages which collectively are known as interphase. Inter = between; phase = …phase, so interphase is just the stage between a cell’s creation and that cell’s division by mitosis.
Interphase is by far the stage in which most cells are in most of the time. The other stage, the small one, is called the mitotic phase and it encompasses mitosis (prophase, metaphase, anaphase and telophase) plus cytokinesis.
Between these various stages in the cell cycle there are multiple opportunities for checkpoints to ensure the cell is undergoing organelle duplication, DNA synthesis,etc. in the right way, before proceeding onto the next stage.
Errors at these checkpoints that serve to control the cell cycle are associated with the development of cancer. The mitotic phase is the cell replication point. Therefore, the G phases allow the adequate monitoring of the cell’s internal and external environment to ensure organelles are in place for division and the cell is operating properly.