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Cell Cycle
Cell division is the basis of reproduction
for every organism. It also replaces
worn-out or damaged cells.
CELL CYCLE – an ordered sequence
of events that extends from the time a
cell is first formed from a dividing parent
cell until its own division into two cells.
Interphase – most of the cell cycle is spent in interphase.
G1 (gap 1) – cell grows
S (synthesis)– cell continues to grow and copies its chromosomes
G2 (gap 2) – grows some more and completes preparations for division
Mitotic phase (M Phase) – cell acutally divides. Consists of mitosis and
cytokinesis.
Interphase
-Cell synthesizes new molecules
and organelles.
-by G2, the cell has doubled its
contents and contains two
centrosomes.
-In the nucleus – chromosomes
are duplicated but can not be
distinguished individually. They
are still loose chromatin.
-nucleus contains nucleoli
(making ribosomes)
Prophase
NUCLEUS – the chromatin becomes
tightly coiled and folded, forming
chromosomes that can be seen with a
light microscope. Nucleoli disappears.
CHROMOSOMES – each chromosome
appears as two identical sister
chromatids joined together (centromere)
CYTOPLASM – spindles (microtubules)
begin to form – growing out from the
centrosomes. Centrosomes move away
from each other.
Prometaphase/Metaphase
PROMETAPHASE
NUCLEUS – nuclear membrane breaks
apart and disappears.
CYTOPLASM – Centrosomes are at
opposite poles. Spindle fibers extend out
and reach the chromosomes.
CHROMOSOMES – Each chromosome has
a kinetochore (at the centromere). Spindle
fibers attach to the kinetochore. Spingle
fibers move the chromosomes toward the
center of cell.
METAPHASE
CHROMOSOMES – the chromosomes convene on
the metaphase plate, an imaginary plane equidistant
between the two poles.
Anaphase
CHROMOSOMES –
-Centromeres or each chromosome come
apart. Sister chromatids are seperated
and are considered daughter
chromosomes.
-Proteins on the kinetochores (powered by
ATP) “walk” the daughter chromosomes
(centromere first) along the spindle fiber
toward opposite poles.
-spindle fibers attached to chromosomes
shorten.
CELL
-cell becomes enlongated.
Telophase
CELL
-elongation continues
NUCLEUS
-daughter nuclei appear at the two poles.
Nuclear membranes (envelopes) from around
the chromosomes.
-Nucleoli reappear
CHROMOSOMES
-chromatin of the chromosomes uncoils.
CYTOPLASM
-spindles disappear
Cytokinesis
“Division of the cytoplasm”
ANIMAL CELL
-occurs by a process called
cleavage. The first sign is the
appearance of a cleavage furrow (a
shallow groove in the cell
membrane). Furrow deepens and
eventually pinches the parent cell
into two.
PLANT CELL
-During telophase, vesicles containing cell
wall material collect at the middle of the
parent cell. The vesicles fuse together,
forming a membrane called the cell plate.
Cell plate grows outward. Membrane around
the cell plate fuses with the cell membrane
and the cell plate’s contents join the parent
cell wall.