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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.
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.
Knowledge of the cell cycle comes in very useful in the treatment of cancer. Cancerous cells divide out of control, often due to mutations in DNA which result in improper regulation of cell division. These mutations have been isolated in certain genes known as oncogenes. The best drugs to treat cancer must be efficient at targeting and killing the cancerous cells, without damaging any nearby healthy cells. When cells divide too quickly, tumour suppressor genes regulate them and give DNA an opportunity to be repaired, or for the immune response to kill the cancerous cells. If the tumour suppressor genes mutate themselves, then the probability of cancer developing increases significantly.
Lovely little topic. Remember the stage of the cell cycle where DNA replicates (interphase->S phase). Also, some cells never undergo mitosis, and so remain in G1 indefinitely. In this particular scenario the cells are said to be in the G0 phase.