Mitosis

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Mitosis

• Year 11 Biology

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• 5. Maintenance of organisms requires growth and
  repair
• Identify mitosis as a process of nuclear division
  and explain its role

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Mitosis

• The process by which cells reproduce for growth
  or tissue repair in multicellular is called cell
  division or mitosis

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Mitosis and Meiosis

• Before mitosis and meiosis can be explained, some
  background information is needed. Inside the cell
  there are many organelles, or small organs.

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• One is the nucleus. Inside the nucleus is the DNA
  that tells the cell what to do. The DNA is found
  in the form of 46 chromosomes that are contained
  in the nucleus. All 46 are blueprints for some
  sort of body part or feature.

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They look like this
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• The other background info needed is the knowledge
  of the cell cycle. Mitosis and meiosis are part
  of the cell cycle. There are 4 parts of the
  cycle. The first 3 are known as interphase.

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• The first part occurs after the cell is born. It
  is called Growth 1 (G1). During this phase the
  cell completes its function as a cell. As it
  metabolizes and grows, it performs the process it
  was meant to do. If it is a lung cell, it helps
  use oxygen, if its a liver cell, it helps the
  liver function, etc.

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• The next phase is the S phase, or Synthesis
  phase. During this time the DNA inside the cell
  replicates, making a total of 92 chromosomes
  inside the nucleus.

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• After replication, the cell enters G2, or Growth
  phase 2. During this phase the cell continues to
  grow and metabolizes. Also, all of the organelles
  are doubled, save for the nucleus. That comes
  next

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• Mitosis is the final step in the cell cycle.
  Basically, it is the division of the nucleus and
  the chromosomes within it. There are 4 steps in
  mitosis and a fifth one that is or isn't part of
  it, depending on what source you get it from.
  First, prophase occurs

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• In prophase, the loosely strung chromatin in the
  nucleus starts to get really tightly wound. It
  becomes so dense and closely coiled that is
  visible under a microscope (chromatin isn't).
  Also, the nucleus starts to deteriorate and the
  centrioles (dormant or non-existent during
  interphase) start sending out spindle fibers.

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• During metaphase, the spindle fibers attach to
  the chromosomes and align them along the middle
  (equator) of the cell (by this time the nucleus
  is completely gone).

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• Anaphase comes next and the chromosomes are
  pulled apart by the spindle fibers. The separated
  sister chromosomes (chromosomes that are
  identical to one another created during DNA
  replication) are pulled to the poles of the cells
  in preparation for telophase, the final step of
  mitosis.

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• In telophase, the chromosomes arrive at the
  poles, the spindle fibers break down, and two new
  nuclei begin to form around the two new groups of
  chromosomes.

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• Also, a cleavage furrow begins to form along the
  outside of the middle of the cell. The disputed
  step is next and is called cytokinesis.

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• Cytokinesis is simply the division of the
  cytoplasm (i.e. the other organelles besides the
  nucleus). The cleavage furrow gets bigger and
  bigger until the cell just splits into two new
  cells. The cell has become two new, identical (to
  each other and to the parent cell) cells that can
  enter the cell cycle. Mitosis is how body cells
  reproduce themselves