13The Cell Cycle

The cells of all organisms undergo division in order to proliferate. In humans, cell division is repeated cyclically from one fertilized ovum to create an adult body made up of approximately 60 trillion cells. Cell division continues thereafter in order to replace old or lost cells and enable metabolic turnover and regeneration. The cell cycle is the cycle of cell proliferation, in other words, the repetitive process of one parent cell dividing to create two daughter cells. The cell cycle phenomenon has been known for long; however, the molecular mechanisms controlling it have only been brought to light gradually over the past 20 years. This chapter introduces the phenomenon of the cell cycle and then continues with the discussion of the basic issues related to the mechanisms underlying the progression of the cell cycle. The cell cycle is not only related to the biological proliferation (see Chapter 2) and replication (see Chapter 7), which were studied earlier, but also to the regulation of signal transduction (see Chapter 15).

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