2.4%20The%20Cell%20Cycle

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2.4 The Cell Cycle
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The Cell Cycle

• The cell cycle is the sequence of events from one
  cell division to another
• Made up of 3 phases
• Interphase
• Cell division
• Mitosis
• Cytokinesis

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PHASE 1 Interphase

• 90 of the time, most of the cells in your body
  are not dividing.
• Instead, they are growing and working.
• cell makes copies of each organelle in the
  cytoplasm
• when it gets big enough it will make copies of
  its chromosomes.

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• Each chromosome and its copy are called sister
  chromatids
• Each sister chromatid carries identical
  instructions for the functions of the cell
• Joined at a region in the center called
  centromere.

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• At some point, the cell gets too large to
  function efficiently and must divide.
• The original cell (parent cell) divides into 2
  genetically identical cells (daughter cells) in
  PHASE 2 CELL DIVISION

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PHASE 2 Cell Division

• is made up of mitosis
• During mitosis, the nuclear material divides.
• The result is 2 nuclei in one cell.
• During PHASE 3 cytokinesis, the cytoplasm and
  the rest of the organelles divide.
• begins before mitosis is finished.

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• Mitosis is a continuous process divided into 4
  stages
• Prophase (P)
• Metaphase (M)
• Anaphase (A)
• Telophase (T)

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Mitosis Overview
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• Prophase
• Chromosomes coil and condense into visible
  threads
• The nuclear membrane breaks down and disappears.
• Sister chromatids become joined at or near the
  center look like an X

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• In animal cells, the pair of centrioles has also
  been duplicated (in interphase)
• each pair moves to opposite poles of the cell.
• Spindle forms between the centriole pairs.
• Plant cells do not have centrioles, but they do
  form a spindle.

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• Metaphase
• Sister chromatids attach to the completely formed
  spindle fibers.
• Paired chromosomes line up along equator

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• Anaphase
• Sister chromatids are pulled apart by the spindle
  
• Each pair splits at the centromere (becomes a
  chromosome).
• One chromosome from each of the previous pairs
  moves to the opposite pole of the cell.

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• Telophase
• The events of prophase happen in reverse
• Nuclear membranes form around the 2 new sets of
  chromosomes.
• Spindle disappears and chromosomes uncoil and
  become invisible again

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• This phase ends when the chromosomes have
  returned to the interphase stage.
• Cytokinesis begins

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PHASE 3 Cytokinesis

• Begins at the end of mitosis, during telophase.
• Divides the cytoplasm into two daughter cells.

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• In animals, the cell membrane indents or pinches
  inwards.
• In plants, the cell forms a cell plate which
  starts in the center and moves towards the outer
  edges to split the cell in two.