![]() ![]() While quiescent cells may re-enter the cell cycle, senescent cells do not. Cells may remain quiescent in G 0 for an indeterminate period of time (when no more new cells are needed), only to re-enter G 1 phase and begin dividing again under specific conditions. Such cells generally enter the G 0 phase from G 1. These cells may be quiescent (dormant) or senescent (aging or deteriorating). Non-replicating cells are found in a stage of the cell cycle called G 0. Not all cells are continually replicated. Of particular significance to the cell cycle, most microtubules – proteins that are required during mitosis – are produced during G 2. During G 2, the cell synthesizes a variety of proteins. Hence, the number of chromosomes in the nucleus, which determines the ploidy, remains unchanged from the beginning to the end of the S phase.įollowing S phase, the cell enters G 2 phase. Note: Chromosomes double their number of chromatids post replication but the nuclei remains diploid as the number of centromeres and chromosomes remains unchanged. Thus, the amount of DNA in the cell has effectively doubled, even though the ploidy, or chromosome count, of the cell remains at 2 n. ![]() Following replication, each chromosome now consists of two sister chromatids (see figure below). During this phase, the cell makes a variety of proteins that are needed for DNA replication.ĭuring S phase, which follows G 1 phase, all of the chromosomes are replicated. Interphase begins with G 1 (G stands for gap) phase. Each stage of interphase has a distinct set of specialized biochemical processes that prepares the cell for initiation of cell division (see figure below). After M phase (discussed below), the daughter cells each begin a new cycle by proceeding to interphase. ![]()
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