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8 Cards in this Set
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Mitosis overview: associated with growth and repair |
~Only four chromosomes are depicted. ~Before nuclear division takes place, DNA replication occurs, duplicating the chromosomes ~Each replicated chromosome is composed of two sister chromatids held together in a region called the centromere ~Sister chromatids are genetically identical—they contain the same DNA sequences ~ At the completion of mitosis, each of the chromosomes in the daughter cells consists of a single chromatid, sometimes referred to as a daughter chromosome. |
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Mitosis is nuclear division that produces two daughter nuclei, each with the same number and kinds of chromosomes as the parental nucleus. |
divided into several phases: prophase, prometaphase, metaphase, anaphase, and telophase |
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Prophase: The centrosomes begin moving away from each other toward opposite ends of the nucleus. Spindle fibers appear between the separating centrosomes as the nuclear envelope begins to fragment, and the nucleolus begins to disappear. The chromatin condenses and the chromosomes are now visible. Each is duplicated and composed of sister chromatids held together at a centromere. The spindle begins forming during late prophase. |
Prometaphase: Kinetochores appear on each side of the centromere, and these attach sister chromatids to the kinetochore spindle fibers. These fibers extend from the poles to the chromosomes, which will soon be located at the center of the spindle. The kinetochore fibers attach the sister chromatids to opposite poles of the spindle, and the chromosomes are pulled first toward one pole and then toward the other before the chromosomes come into alignment. Notice that even though the chromosomes are attached to the spindle fibers in prometaphase, they are still not in alignment. |
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Metaphase: the fully formed spindle consists of poles, asters, and fibers. The metaphase plate is a plane perpendicular to the axis of the spindle and equidistant from the poles. The chromosomes attached to centromeric spindle fibers line up at the metaphase plate during metaphase. Polar spindle fibers reach beyond the metaphase plate and overlap. |
Anaphase: the centromeres uniting the sister chromatids divide. Then the sister chromatids separate, becoming daughter chromosomes that move toward the opposite poles of the spindle. Daughter chromosomes have a centromere and a single chromatid.What accounts for the movement of the daughter chromosomes? First, the kinetochore spindle fibers shorten, pulling the daughter chromosomes toward the poles. Second, the polar spindle fibers push the poles apart as they lengthen and slide past one another. |
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Telophase: the spindle disappears, and nuclear envelope components reassemble around the daughter chromosomes. Each daughter nucleus contains the same number and kinds of chromosomes as the original parental cell. Remnants of the polar spindle fibers are still visible between the two nuclei. The chromosomes become more diffuse once again, and a nucleolus appears in each daughter nucleus. Cytokinesis is under way, and soon there will be two individual daughter cells, each with a nucleus that contains the diploid number of chromosomes. |
Cytokinesis, or cytoplasmic cleavage, usually accompanies mitosis, but they are separate processes. Division of the cytoplasm begins in anaphase and continues in telophase but does not reach completion until just before the next interphase. |
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As with animal cells, mitosis in plant cells permits growth and repair. A particular plant tissue called meristematic tissue retains the ability to divide throughout the life of a plant. Meristematic tissue is found at the root tip and also at the shoot tip of stems. Lateral meristematic tissue accounts for the ability of trees to increase their girth each growing season. |
Although plant cells have a centrosome and spindle, there are no centrioles or asters during cell division. The spindle still brings about the distribution of the chromosomes to each daughter cell. |
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Cytokinesis in animal cells. A single cell becomes two cells by a furrowing process. A contractile ring composed of actin filaments gradually gets smaller, and the cleavage furrow pinches the cell into two cells. |
The rigid cell wall that surrounds plant cells does not permit cytokinesis by furrowing. Instead, cytokinesis in plant cells involves building new cell walls between the daughter cells. |
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Animal cells form a cleavage furrow between the daughter nuclei, which is constricted by the action of a band of actin filaments. Plant cells build a new cell wall between the daughter cells by fusing together vesicles produced by the Golgi apparatus. |
Both result in two daughter cells with identical genetic material. |
