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CHAPTER 10 NOTES
MITOSIS
Why do cells only grow to a certain
size before they have to divide?
1. “DNA Overload”: large cells would
require more DNA (to make the
necessary proteins) than can be
supported by a single nucleus.
2. Exchanging materials: as a cell
grows, its volume increases much
faster than its surface area so the
amount of materials needed to
support a large cell can not diffuse
through the cell membrane.
The cell cycle is the series of events
that cells go through as they grow
and divide.
Consists of 4 phases:
1. G1 phase : period of growth.
2. S phase: DNA replicates itself.
3. G2 phase: the cell prepares for
mitosis.
4. M phase: period of division which
includes mitosis and cytokinesis.
DNA goes through changes during the
cell cycle:
• Called chromatin
• DNA is uncoiled
• Invisible under the
microscope
• Looks like this
during interphase
• DNA coiled up like a
slinky
• Visible under the
microscope
• Called two sister
chromatids
• Sister chromatids are
held together by a
centromere
• Looks like this during
prophase and metaphase
• Two sister
chromatids
separate
• Each is now called
a chromosome
• Looks like this
during anaphase
and telophase
INTERPHASE
Gap 1(G1):
• the cell grows in size
• protein production is high
• the longest part of the cell cycle
Synthesis (S):
• the chromosomes copy themselves in
a process called DNA synthesis or
Replication.
Gap 2 (G2):
• organelles are made
• cell parts needed for division are
made (centrioles)
• usually the shortest part of the cell
cycle.
MITOSIS
Definition: the division of the
nucleus
Prophase
• chromatin coils up or condenses into
visible double chromosomes (two
sister chromatids).
• the nuclear envelop and nucleolus
disappear.
• the centrioles begin to migrate
toward the poles (animal cells only).
• the spindle (a foot-ball shaped
structure) begins to form and the
fibers attach to the centromeres of the
sister chromatids.
Metaphase
• the doubled chromosomes line up at
the equator (middle) of the cell
moved by the spindle fibers attached
to their centromere.
Anaphase:
• the centromeres split separating the
sister chromatids.
• the spindle fibers pull the identical
chromosomes towards the opposite
poles.
Telophase: mainly the opposite of
prophase
•
•
•
•
the chromosomes uncoil and become invisible.
the nuclear envelopes and nucleolus reappear.
the spindle fibers break down and disappear.
The cytoplasm begins to divide (cytokinesis).
CYTOKINESIS
Definition: the division of the
cytoplasm
Animal cells: the plasma membrane
pinches in along the equator causing
a furrow. The furrow deepens until
the cell is pinched in half.
Plant cells: a cell plate develops along
the equator of the cell and grows
outward until it reaches the cell wall.
New cell wall material is secreted on
each side of the cell plate until
separation is complete.