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    Stages of the Cell Life Cycle

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    Discuss the cell life cycle through various stages as chromosomes are replicated ending in the division of the cell's cytoplasm.

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    The Cell Life Cycle

    The cell life cycle is a series of changes that a cell goes through from the time it is forms until reproduces itself. This cycle is divided into two major periods: interphase and the mitotic phase.

    The interphase cycle is when the cell grows and carries on its usual activities. In addition, the interphase cell prepares the cell for the next cell division. It is divided into three parts: G?, S, and G?. During G? or growth 1, which is the first part of interphase, cells are metabolically active, synthesize proteins rapidly, and growing rapidly. The G? part lasts for several hours however, in cells that divide at a slow pace, it may last for days or years. For the most growth 1, none of the cell activities are directly related to cell division occurs. However, near the end of the G?, the centrioles start to replicate preparing for cell division. The S (synthetic) stage is when DNA replicates itself with two future cells receiving identical copies of the genetic material. In the final stage of interphase, called G? (growth 2), the enzymes needed for the division process are synthesized. The centrioles finish copying themselves at the end of this stage. Through the last two stages, the cell is continuing to grow and carry on its normal metabolic activities. (Marieb & Mallatt, 1997)

    Cell Division
    Cell division is important for body growth and tissue repair. Cells divide in the M (mitotic) phase of their life cycle which is followed by interphase. Cell division therefore involves two events: mitosis and cytokinesis.

    Mitosis is a series of events that take place in 6 stages. During mitosis, replicated DNA of the original cell is distributed out to two new cells, resulting in the division of the nucleus. During these events, chromosomes are seen as thick rods. Even before mitosis can take, the cells need to have stored enough energy to go through the chemical processes. The six stages of mitosis are: interphase, early prophase, late prophase, metaphase, anaphase, and telophase.

    The period of a cell's life where it is carrying out its normal metabolic activities and growing. During this stage, DNA has replicated but is loosely coiled as chromatin. The centrioles begin replicating, and the nuclear membrane and nucleolus are still intact and visible.

    Early prophase
    During prophase, which is the first and longest stage of mitosis, the chromatin threads start to coil and condense forming chromosomes. The chromatin threads have formed into two identical threads called chromatids held together by a centromere.

    Late prophase
    At this stage, the nucleus is no longer visible and the centriole pairs separate from each other. The centrioles act as focal points for growth of microtubules called mitotic spindles. The centrioles are pushed further apart as the microtubules lengthen going to opposite ends of the pole. In addition, the spindle microtubules attach to special protein complexes called kinetochores. So the most important activity in this stage is the spindle microtubules moving to opposite ends of the pole.

    In this stage the spindle fibers attach themselves to the chromosomes and align at the equator or center of the metaphase plate ("The Stages of Mitosis", 2012).

    The spindle fibers shorten and pull each chromosome towards the pole it faces. Polar fibers lengthen and push two poles of the cell apart. This stage is easy to recognize because the moving chromosomes look V-shaped. Therefore, during this stage the chromosomes are noted as daughter chromosomes.

    The chromosomes during telophase reach the opposite poles uncoiled and go back to their threadlike chromatin form. A new nuclear membrane reforms around the chromatin mass. The nucleoli reappear within the nuclei and the spindles break and disappear ("The Stages of Mitosis", 2012).

    This is considered the last stage of mitosis. Cytokinesis is the division of the cytoplasm completing the separation of one cell into two. A ring of contractile microfilaments in the center of the original cell constricts pinching the cell into two. The two cells are called daughter cells entering the interphase part of the cell's life cycle.

    Marieb, E. N. Mallatt, J. (1997). Human Anatomy (2nd ed). California: Benjamin/Cummings.

    "The Stages of Mitosis" (2012). Retrieved May 17, 2012

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