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UNIT 2 PART 2: CELL DIVISION
• All cells come from other cells.
• Each round of cell growth and division is
called the cell cycle.
• For unicellular
organisms, this is
reproduction
because it results
in a new individual.
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In a cell with a nucleus two
processes take place:
• Mitosis
– The division of the
nucleus
– It has four stages
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
• Cytokinesis
– The division of the
cytoplasm
– Forms two
separate cells
– These cells are
genetically identical
Before mitosis the cell must grow and
prepare. This happens during Interphase,
where the cell spends most of its time.
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Interphase
• From the end of one
division to the
beginning of the next:
G1, S, and G2.
• This is when the cell
grows, makes more
organelles and
proteins, and replicates
the chromosomes so
they become doubled.
• Centrioles in animal
cells also replicate.
• During Interphase, the
chromosomes are
uncoiled, not visible,
and called chromatin.
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• Doubled chromosomes
become visible.
Prophase
– Each strand is called a
chromatid.
– The chromatids are connected
by a centromere.
• Centrioles move to the poles.
• Microtubules form asters and
the spindle apparatus that
stretches from pole to pole.
• Nuclear membrane and
nucleolus disappear.
chromatids
4
Metaphase
• Centromeres, which
are connected to
spindle fibers, line up
in the middle of the cell
on the metaphase, or
equatorial, plane.
• By the end of
metaphase the
centromeres divide
and the chromatids
become separate
chromosomes.
5
Anaphase
• The chromosomes
are pulled to
opposite poles by
the spindle fibers so
that there is one
complete set at
each end of the cell.
6
Telophase
• The chromosomes
reach the poles and will
uncoil again into
chromatin.
• The spindles and
asters disappear.
• A nuclear membrane
forms around each set
of chromosomes
forming two daughter
nuclei.
• Nucleoli reappear.
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Cytokinesis: The formation of two
separate identical cells
• In animal cells the cell
membrane pinches in
until opposite sides
touch and two new
cells are formed.
• In plant cells a cell
plate forms between
the two daughter
nuclei and forms a
new cell wall.
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MITOSIS REVIEW - IPMAT
• Interphase – chromatin
and replication of DNA
• Prophase –
chromosomes visible
• Metaphase – lined up in
the middle
• Anaphase –
chromosomes move
• Telophase – two new
nuclei form
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Mitosis Animation
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Some Mitosis Facts
• The two daughter cells made from mitosis are
identical to each other and the parent cell.
• Mitosis happens most often in least
specialized cells like early embryos.
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Some Mitosis Facts
• Specialized cells like xylem, muscle, and
nerve cells rarely, if ever, divide.
• Places of growth like root tips, bone
marrow, and skin have cells that divide
rapidly.
• A protein called cyclin regulates the cell
cycle.
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