![]() Cells in either mitosis or cell division (also called cytokinesis) are in the M phase, whereas those in the other three phases (G1, S, and G2) are in the interphase. This is followed by mitosis (M) and cell division, which leads to the formation of two diploid daughter cells. After DNA replication is completed in the S phase, the cell enters the G2 phase and has twice the amount of the DNA (4N) of the starting cell. The cell cycle begins in the G1 phase of a diploid cell (DNA content = 2N N is the number of chromosomes). Of these, the M phase takes approximately one hour to complete and interphase takes up the remaining 23 hours.įigure 15.1. Typically, the amount of time required for a single cell cycle in actively proliferating human cells in culture is 24 hours. The M phase is in turn comprised of two processes: mitosis, in which the cell’s chromosomes are equally divided between the two daughter cells, and cytokinesis (or cell division), in which the cytoplasm of the cell divides in half to form two distinct daughter cells. The DNA content of a cell in the S phase varies between 2N and 4N, depending on the stage of replication of the cell. The DNA content of a cell in the G 1 phase is 2N (N is the number of chromosomes), also known as diploid, whereas the DNA content of a cell in the G 2 phase is 4N (tetraploid). The G 1, S, and G 2 phases collectively make up the interphase. The four phases of the cell cycle are G 1 (G for gap), S (synthesis), G 2, and M (mitosis) ( Figure 15.1). Other checkpoints detect problems that arise during attachment of chromosomes to the spindle.Ī typical eukaryotic cell cycle contains several distinct phases that progress in an orderly fashion - a phase cannot commence without completion of the previous phase. ![]() Checkpoints detect damage to the DNA due to external agents or problems that arise during DNA replication and trigger the DNA damage response. These nondividing cells (which may physiologically be extremely active) are in the G 0 phase, a branch of the G 1 phase.Ĭheckpoints: Biochemical circuits that regulate cell-cycle transitions in response to the physiological condition of the cell and signals from its environment. In multicellular organisms, many differentiated cells no longer actively divide. The G 2 (second gap) phase is the interval between the termination of DNA replication and the onset of mitosis. The S (synthetic) phase is the time when DNA is replicated. The G 1 (first gap) phase is the interval between mitosis and the onset of DNA replication. Interphase: The portion of the cell cycle when cells grow and replicate their DNA. In general, each daughter cell receives a complement of genetic material and organelles identical to that of the parent cell. M phase: Cell division, comprising mitosis, when a fully grown cell segregates the replicated chromosomes to opposite ends of a molecular scaffold, termed the spindle, and cytokinesis, when the cell cleaves between the separated chromosomes to produce two daughter cells.
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