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How does the cell know how and when to commence DNA replication?

Most of the time the signals are chemical. Cells follow "rules of behavior", one of which is called contact inhibition. When cells are being touched on all sides (except sometimes the top when in a culture dish or at the surface of the skin) they are not dividing. As soon as a cell is damaged or dies, chemicals are released that signal the cell to begin replicating it DNA and then the cell divides to make a new cell.


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