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The Cell Cycle

The Cell Cycle. The “life span” of a cell can be broken up into 3 distinct parts While distinct, note that the stages occur continuously, one after another. Interphase. Longest phase Also called the resting phase

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The Cell Cycle

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  1. The Cell Cycle • The “life span” of a cell can be broken up into 3 distinct parts • While distinct, note that the stages occur continuously, one after another

  2. Interphase • Longest phase • Also called the resting phase – however, there is still cell activities occurring, like respiration, growth and repair • Chromosomes appear as threads of chromatin that cannot be seen under the microscope

  3. Interphase Toward the end of interphase, just before mitosis is to occur: • Centrioles in an animal cell replicates (now 2 pairs) • Chromatin threads replicate, producing 2 identical chromatin threads joined at the centromere • Chromatin start to coil and condense to form chromosomes (can now be seen under light microscope) Chromatin thread Centromere Chromosome

  4. Stages of Mitosis • After the resting phase, cells undergo mitosis • Mitosis consists of 4 stages

  5. Prophase • Early prophase: • Chromatin threads complete condensing and coiling to form chromosomes which consists of sister chromatids joined at the centromere • Centrioles move to opposite poles of the cell • Asters (made of microtubules) form around the centrioles • Nucleolus in nucleus disappears

  6. Prophase • Late prophase: • Nuclear envelope disappears • Spindle fibres made from the microtubules form the spindle Nuclear envelope disappears Spindle made from spindle fibres

  7. Metaphase • Chromosomes line themselves up along the equator of the spindle • Each centromere becomes attached to one spindle fibre

  8. Anaphase • Centromeres split • Spindle fibres pull the sister chromatids apart to opposite poles of the cell • Sister chromatids are now known as daughter chromosomes

  9. Telophase • Spindle fibres break down • Nuclear envelopes form around the chromosomes at each pole of the cell • Nucleolus forms at each pole of the cell • Chromosomes uncoil and lengthen to form chromatin threads again

  10. Cytokinesis • The division of cytoplasm occurs • Begins to happen during telophase • Cleavage furrow appears between the 2 poles of the cell • Cleavage furrow deepens until 2 identical daughter cells are produced • In plant cells, cleavage furrows in the cytoplasm do not occur due to the presence of the cell wall • Instead, small fluid-filled vesicles from the Golgi apparatus move between the 2 poles and fuse to form a cell plate

  11. Cytokinesis

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