Only when all sister chromatids have been bound will mitosis proceed into anaphase. The third checkpoint, also known as the spindle apparatus checkpoint, is inflienced by attachment of the mitotic spindle to all chromosomes. The G2/M checkpoint, also known as the DNA replication checkpoint, is influenced by improper DNA replication or DNA damage. During the G1/S checkpoint, also known as the restriction checkpoint, primary influencers of cell cycle progression include growth factors, DNA damage, cell size, and cell nutrition. There are three main checkpoints in mitosis, and those include the G1/S checkpoint, G2/M, and metaphase/ anaphase checkpoint. If any of these checkpoints are bypassed without being complete, certain pathology, such as cancer, can occur. If certain conditions are not met, mitosis halts. Throughout mitosis, certain checkpoints are essential to the continuation of the process. In animal cells, this is accomplished through a cleavage furrow that pinches the cell in 2. Lastly, cytokinesis, which is the division of the cytoplasm, takes place and the cell divides into 2 separate cells. Mitosis, the division of one nucleus into 2, is now complete. DNA begins to de-condense while spindle microtubules begin to depolymerize. By the end of anaphase, the 2 halves of the cell have an equivalent collection of chromosomes. In anaphase, the shortest stage of mitosis, the sister chromatids break apart, and the chromosomes begin moving to opposite ends of the cell. The metaphase plate is an imaginary line equidistant from the spindle’s 2 poles. The chromosomes have all lined up at the metaphase plate in the middle of the cell, and all chromosomes are attached to microtubules through their kinetochores. In metaphase, the centrosomes have migrated to opposite poles of the cell. Some microtubules interact with microtubules extending from the other side of the cell. Not all microtubules interact with kinetochores. The microtubules bind at the kinetochores, specialized protein structures at the centromere. In prometaphase, the nuclear envelope falls apart microtubules can now invade the nuclear area and bind to some of the chromosomes. Also, the centrosomes begin to move to opposite poles of the cell, and they are propelled by the lengthening microtubules between them. In prophase, the chromatin fibers condense into chromosomes that are visible through a light microscope, each replicated chromosome appears as two identical sister chromatids joined at their centromeres, and the mitotic spindle begins to form. Centrosomes organize the fibers of the mitotic spindle during mitosis that will help pull the sister chromatids apart. To organize the chromsome motion in the cell to help make division efficient as well as ensure all material is present in both daughter cells, the cell has centrosomes at each pole of the cell. In interphase, a nuclear envelope surrounds the nucleus, the DNA is replicated in the S phase, and the sister chromatids join together at the central portion of the chromosome - the centromere. Mitosis is conventionally divided into 5 phases, which include prophase, prometaphase, metaphase, anaphase and telophase and cytokinesis. Mitosis occurs during M phase, which occurs after interphase. During the S phase, the cell replicates its genome in preparation for cell division or mitosis. During these phases, the cell grows by producing various proteins and cytoplasmic organelles. The largest portion of the cell cycle, interphase, makes up 90% of a cell's life cycle, and is the stage for growing and performing the cellular functions specific to that cell. The interphase is further divided into two G phases- G1 and G2- and an S phase. The mitotic phase is usually the shortest part of any cell cycle.
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