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Mitosis

Mitosis. The Cell Cycle. Cells go through a continual process of growth, repair, and division, collectively called the cell cycle Mitosis is merely a small portion of the cell life-cycle Varies cell to cell, but most cells spend approximately 90% of their life in interphase. Interphase.

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Mitosis

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  1. Mitosis

  2. The Cell Cycle • Cells go through a continual process of growth, repair, and division, collectively called the cell cycle • Mitosis is merely a small portion of the cell life-cycle • Varies cell to cell, but most cells spend approximately 90% of their life in interphase

  3. Interphase • Begins with the G1 (stands for first gap) stage • Proteins are created during this time, but DNA is not replicated • Still in chromatin form • Cell continues to grow in size • Possible to stop during this phase, in a sort of stasis called G0 • During this time, cells can become totipotent • Important concept in cloning

  4. Neurons, muscle cells and other cells that are non-proliferating will stay in this phase for extended periods of time • Next is S (synthesis) phase • DNA is replicated • Chromosomes are now made of two sister chromatids (identical copies of each other)

  5. Finally, cell enters G2 (second gap) phase • Cytoplasmic organelles are replicated • Cell is now prepared to go through mitosis • But, we ask, “why?” • Compare surface area rate of change to volume rate of change • Increased volume, increased number of organelles, increased demand for nutrients • Membrane plays important role in absorption of nutrients

  6. Mitosis • Broken into 4 (or 5!) distinct stages Prophase • Chromatin condenses and coils to the point where it is visible chromosomes, linked by centromere • Nuclear envelope dissolves • Mitotic spindle forms

  7. Prometaphase • Not really a distinct phase • Kinetochores form around centromeres, some spindles attach Metaphase • Centrosomes at opposite ends of cells (called poles) • Chromosomes begin to line up at center of cell – forms metaphase plate • Kinetochores point to opposite poles

  8. Anaphase • Centromeres separate, copied chromosomes move to opposite ends of cell • Sister chromatids are now called daughter chromosome Telophase • Final stage of mitosis (not cytokinesis!) • Daughter chromosomes at opposite poles • Spindle fibers dissolve • Nuclear membrane reforms

  9. Cytokinesis • Cells no longer in mitosis • A contractile ring of actin filaments begins to pinch the equator of the cell – cleavage furrow forms • Microtubules reorganize into a new cytoskeleton

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