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

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”!

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!

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

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

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!

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

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)