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mitosis

mitosis The Process of Mitosis is the term used to describe cell division for replication. The product at the end of mitosis is two daughter cells both genetically identical to the original (parent) cell. This process is used for growth and repair within an organism and also for asexual reproduction. There are five main stages to mitosis, called Interphase, Prophase, Metaphase, Anaphase and Telophase. Although the process has been divided up into these stages the process of mitosis is actually continuous. In Interphase, the first stage, the cell will look just like any other 'normal' cell although this is far from the case because very much is actually happening. All cell organelles are being produced in quantity and the chromosomes (DNA molecules) are being copied exactly. The two identical copies of DNA are called a pair of chromatids and they are linked together by an item called a chromomere. During this stage a store of ATP is also built up In Prophase changes to the cell become visible. The chromosomes condense, coiling up to about 5% of their original length and are now clearly visible when a stain is added. The centrioles move to the opposite poles of the cell and small microtubules around the centrioles become visible. The nuclear membranes and nucleolus disintegrate after passing their nucleic acids to certain pairs of chromatids. Now a spindle forms, this is also made out of microtubules. During Metaphase, the chromosomes move towards the equator of the spindle, attaching themselves horizontally by the centromere to the spindle's filaments. The chromatids then pull slightly away from each other at the centromere towards the opposite poles of the cell. Some spindle fibers run from pole to pole while others from pole to equator. Anaphase, the next step, is very quick. The pairs of chromatids are separated and each chromatids is pulled is pulled towards each opposite pole by the spindle fibers by a ratchet-like mechanism. This process requires energy so the ATP store is now used up. They split apart by the centromere breaking into two. Each centromere divides into two so that each chromatid has its own centromere. In Telophase, the chromatids become the new chromosomes of the daughter cells. Once the chromatids are at the poles of the cell they unwind into chromatin again, now becoming hard to see once again. The spindle fibers now disintegrate and new nuclear membranes form around the new groups of chromatin making two new nucleus'. The centrioles now also replicate and divide their numbers evenly around each nucleus. Now the cell is ready to divide. Mitosis is now over. The cell is now ready to divide, by the process known as Cytokinesis. Bibliography:

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