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Cell Cycle

Cell Cycle. Repeating cycle of growth and division Interphase —takes up ~ 80% of cell’s life; 3 phases G1 —cell is rapidly growing and carrying out routine functions (longest) S —synthesis phase when DNA replicates from a single chromatid into a full chromosome

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Cell Cycle

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  1. Cell Cycle • Repeating cycle of growth and division • Interphase—takes up ~ 80% of cell’s life; 3 phases • G1—cell is rapidly growing and carrying out routine functions (longest) • S—synthesis phase when DNA replicates from a single chromatid into a full chromosome • G2—organelles replicate and chemicals needed for mitosis are produced and sent to proper locations within the cell

  2. Cell Division and Mitosis • When a cell becomes too large to function properly due to surface area-to-volume ratio it will be stimulated to divide • Prokaryotic cells (bacteria) undergo binary fission: asexual reproduction that produces identical daughter cells • Can occur every 20 minutes!! • First the single circular strand of DNA replicates, then the cell divides into 2 cells that are identical in every way—think “cloning”!

  3. Eukaryotic Mitosis and Cell Division • Due to all the organelles in eukaryotes, process more complex • Mitosis—nuclear division—nucleus divides into 2 identical nuclei; made of 4 phases • Replaces old cells in an organism • Replaces damaged cells • Remembered by the acronym: PMAT • Occurs only in somatic cells—gametes are a whole another process!

  4. P = Prophase • Chromosomes begin to condense into fuzzy X’s and are visible under a light microscope • Nuclear membrane starts to dissolve • Centrioles start to move apart to opposite sides of cell • Spindle fibers (protein microtubules) form between centrioles—these fibers help pull the chromosomes apart later • Plants do not have centrioles, but they do have spindle fibers

  5. M = Metaphase • Second set of spindle fibers extend out from each chromosome’s centromere—2, one in each centriole direction • Grow until they reach the first set of spindle fibers • Spindle fibers line the chromosomes up at the center (equator) of the cell

  6. A= Anaphase • Centromeres divide and the 2 chromatids separate • Spindle fibers shorten and the chromatids move toward opposite sides of the cell • Looks like centrioles are reeling them in as if fishing!

  7. T = Telophase • Chromatids undergo name change and are now called chromosomes again • Chromosomes start to uncoil at opposite sides of cell • New nuclear membranes form around them • Spindle fibers break and dissolve

  8. Cytokinesis • Cell then starts to divide: cytoplasm is split into 2 new cells • In animals a cleavage furrow forms between the nuclei—cytoplasm is pinched in half • In plants vesicles (created by Golgi bodies) fuse at center of the cell and form a cell plate • New cell wall is created on either side of the plate • In both plants and animals, the 2 new cells each have their own organelles (formed during G2)

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