Transcript Cell Cycle ppt

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)