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. Antibody microinjection resulted in mitotic inhibition in a stage-specific and dosedependent manner, indicating that the protein is an essential spindle component.The mitotic phase is usually the shortest part of any cell cycle. This 95/105 kDa antigen represents a unique component of the spindle distinct from any of the other MAPs reported so far. We have recently identified a novel mitosis-specific microtubule-associated protein (MAP) using a monoclonal antibody probe raised against the mitotic spindles isolated from cultured mammalian cells. Evaluation of the roles of these molecules in both the formation and in the dynamics of spindle microtubules should be important for understanding the molecular basis of mitosis and its regulation. Biochemical, immunological and genetic analyses of mitotic cells have allowed us to identify a variety of molecules that are recruited to form the spindle at the onset of mitosis. They are transient and hence quite labile structures, changing their morphology even while performing their function. Mitotic spindles constitute the machinery responsible for equidistribution of the genetic material into each daughter cell during cell division.
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