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)