Figure 263

Cell cycle. This diagram illustrates the cell cycle of rapidly dividing cells in relation to DNA synthesis. After mitosis, the cell is in interphase. C, represents the period during which a gap occurs in DNA synthesis. S represents the period during which DNA synthesis occurs. During this phase, tritiated thymidine can be incorporated into the DNA to serve as an experimental tracer. G2 represents a second gap in DNA synthesis. G0 represents the path of a cell that has stopped dividing; however, such a cell may reenter the cell cycle at the R point after an appropriate stimulus. The cell residing in G0 may undergo terminal differentiation, GTD. and produce a population of permanent nondividing cells (e.g., adult neurons). The average timing of each phase of the cell cycle is indicated on the diagram.

permanent nondividing cells metaphase mitosis M

quiescent

(stable)

cells

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