FIGURE 5.

Cell cycle and Na⁺. Actively proliferating eukaryote cells pass through four phases of the cell cycle. Cellular contents (excluding chromosomes) are duplicated in first gap phase (G1). Each chromosome is duplicated in synthesis phase (S). Duplicated chromosomes are “error checked” during second gap phase (G2). G1, S, and G2 are collectively called interphase. Equal division of duplicated nuclear material occurs in mitosis phase (M). Division of parent cell into two daughter cells (cytokinesis) completes the cell cycle. If nutrients are limiting or the cells are fully differentiated due to internal genetic programming, cells exit interphase and enter a “resting phase” (G0).