Nuclear envelopes form around the chromosomes, and nucleosomes appear within the nuclear area. The cell becomes visibly elongated (oval shaped) as the polar microtubules slide against each other at the metaphase plate where they overlap.ĭuring telophase, the chromosomes reach the opposite poles and begin to decondense (unravel), relaxing into a chromatin configuration. Each chromatid, now called a chromosome, is pulled rapidly toward the centrosome to which its microtubule is attached. At this time, the chromosomes are maximally condensed.ĭuring anaphase, the sister chromatids separate at the centromere. Eventually, all the sister chromatids will be attached via their kinetochores to microtubules from opposing poles.ĭuring metaphase, all the chromosomes are aligned in a plane called the metaphase plate, or the equatorial plane, midway between the two poles of the cell. Once a mitotic fiber attaches to a chromosome, the chromosome will be oriented until the kinetochores of sister chromatids face the opposite poles. The proteins of the kinetochore attract and bind mitotic spindle microtubules.ĭuring prometaphase, the nuclear envelope is fully broken down and chromosomes are attached to microtubules from both poles of the mitotic spindle, which begin to move them toward the middle of the cell. Each sister chromatid develops a protein structure called a kinetochore in the centromeric region (Figure 3). The sister chromatids begin to coil more tightly and become visible under a light microscope. Microtubules that will form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen. The centrosomes begin to move to opposite poles of the cell. Stages of mitosisĭuring prophase, the “first phase,” the nuclear envelope starts to dissociate into small vesicles, and the membranous organelles fragment and disperse toward the periphery of the cell. Karyokinesis, also known as mitosis, is divided into a series of phases-prophase, metaphase, anaphase, and telophase-that result in the division of the cell (Figure 2).
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