Extended Definition of Mitosis Mitosis: What Keeps Life Going Mitosis is the asexual reproduction of all living sematic cells. Sematic cells are all cells other than reproductive sperm and egg cells. The reason that mitosis is asexual is because it does not require another cell to fertilize it for the process of division. Mitosis is about ten percent of the cells life cycle, the shortest part of the cell’s life. In adult humans it can take up to twenty-­‐four hours to complete one cells life cycle, mitosis would take less than one hour. The longest time of a cell’s life is called interphase and its purpose is to allow the cell to grow, replicate its genetic blueprint called DNA and prepare for mitosis. Mitosis is one part of the mitotic phase, which also includes cytokinesis, the splitting of the cell’s cytoplasm into two separate identical daughter cells. Mitosis is technically the division of one cells nucleus into two separate identical daughter nuclei. When Does Mitosis Begin? Why Do Cells Go Through Mitosis? Mitosis begins at conception for animals. The first cell of a new organism is called a zygote. This zygote begins interphase immediately and then begins dividing into another identical cell producing two daughter cells. The organism has now gone from a single celled organism to a multicellular organism, doubling its mass. The organism will continue to divide its cells and doubling its mass until it reaches maturity as an adult. Mitosis will then begin to happen only to sustain the organism by replacing damaged or deceased cells. What Happens During Mitosis? The mitotic phase is broken up into two parts, mitosis and cytokinesis. Mitosis is further divided into five sub-­‐phases: prophase, prometaphase, metaphase, anaphase, and telophase respectively. Prophase: DNA tightly coils (become visible under microscope) and become sister chromatids (identical chromosomes matched up in pairs). Centrosomes move toward opposite poles of the cell PROMETAPHASE Prometaphase: The nuclear envelope fragments and dissipates. Sister Chromatids are fully condensed. Microtubules attach to the chromosomes at the kinetochore, a specialized region of the sister chromatids where they are connected. Metaphase: Sister Chromatids are moved onto http://www.dartmouth.edu/~cbbc/courses/bio4/bi
plate o4-­‐lectures/images/mitosis.JPG resembles the equator of the earth) Centrioles are at opposite poles of the cell. Anaphase: the two sister chromatids are pulled apart by the microtubules. Now each side of the cell has an exact replica of DNA so both daughter cells will be identical. The cell begins to elongate preparing for cytokinesis. Telophase: Two daughter nuclei begin to form from the nuclear envelope fragments, which broke up in prometaphase. Now mitosis, the division of DNA from one nucleus into two identical daughter nuclei is complete. Cytokinesis: the division of the rest of the cell, its’ cytoplasm and all organelles has already begun by telophase. The cell creates a cleavage furrow (in animal cells) which pinches off the cells membranes and creates two identical daughter cells. Mitosis is now complete, or more accurately, the mitotic phase is now complete. Both daughter cells will continue through interphase until they are ready to divide through mitoses again. ***NOTE: Mitosis should never be mistaken for meiosis, the cell division of gametes (reproductive cells) which is an entirely different process and should be considered separately from mitosis.