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Unformatted text preview: Cell Reproduction: Mitosis - 1 Growth and reproduction are two of the characteristics of life. The cell theory states "All cells come from preexisting cells by a process of cell reproduction, or cell division". Cell division is the process by which all cells of a multicellular organism are formed. Cell division is also responsible for repair and replacement of cells and tissues during one's lifetime. Asexual reproduction, a means of making more individuals is from a single "parent" common in protists, fungi, many plants and some animals. Both prokaryotes and eukaryotes have a process of cell division, although the details are a bit different. The process of cell division must ensure that new cells formed have the genetic information of the original cell and other cellular components from the cytoplasm needed to sustain the cell. In our discussion of cell reproduction, we shall focus on the processes of cell reproduction (mitosis and cytokinesis) in eukaryotic organisms. The process of cell division in prokaryotic organisms, binary fission, has similarities, but the single molecule of DNA and absence of a nucleus in the prokaryotic cell account for a number of differences in the "mechanics" of the process. Mitotic Cell Division We know that all cells of an individual have exactly the same DNA, and their DNA is found in structures called chromosomes. Each eukaryotic species has a fixed chromosome number, a number that does not change from generation to generation. The DNA must also stay the same from cell to cell within an organism, so that when cells divide, new cells formed will have exactly the same DNA as the original cell. To ensure that chromosomes and DNA remain the same in new cells, the following must take place when cells divide: We must form two new cells from the original cell. Since each cell must have all of the genetic material for the organism, we must have a mechanism that exactly duplicates the DNA from the original cell and distributes the copied DNA equally to the new cells. The distribution of DNA into new nuclei during cell division is called mitosis. (Duplication of DNA is a part of the discussion of structure and function of DNA.) We must also separate the cytoplasm, and critical organelles, such as mitochondria and chloroplasts, of the original cell into the new cells formed so that the new cells can survive, grow and function. The separation of cytoplasm into new cells is called cytokinesis. In addition, in sexually reproducing organisms, a variation of cell reproduction, called meiosis, occurs at one stage in the organism's life cycle (to form gametes in animals, or to start the gamete producing stage in plants). We will discuss the process of meiosis later. Cell Reproduction: Mitosis - 2 Before discussing how cells divide, it's probably useful to discuss the structure of chromosomes and chromosome terms (of which there are a sufficiency)....
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