| Figure 30.5 shows the various phases of the growth and division of cells, known as the cell cycle. The G1 phase is a period of cell growth that occurs prior to DNA replication. The phase during which DNA is synthesized or replicated is termed the S-phase. A second growth phase, termed G2, occurs after DNA replication, but prior to cell division. The mitosis or M phase is the period of cell division. Following mitosis, the daughter cells either re-enter the G1 phase or enter a quiescent phase termed G0, where growth and replication cease. The passage of cells through the cell cycle is tightly controlled by a variety of proteins termed cyclin-dependent kinases (for details see Chapter 41).
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