Download Notes for Cell Cycle

CHAPTER 10 NOTES
MITOSIS
Why do cells only grow to a certain size
before the 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.
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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
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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.
Structural Changes of DNA:
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DNA goes through changes during the cell cycle:
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chromatin
DNA is uncoiled
Invisible under the microscope
Looks like this during interphase
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DNA coiled up like a slinky
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Visible under the microscope
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Called two sister chromatids
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Sister chromatids are held together by a centromere
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Looks like this during prophase and metaphase
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Two sister chromatids separate
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Each is now called a chromosome
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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
Interphase:
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Synthesis (S):
· the chromosomes copy themselves in a process called
DNA synthesis or Replication.
Interphase:
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Gap 2 (G2):
· organelles are made
· cell parts needed for division are made (centrioles)
· usually the shortest part of the cell cycle
Mitosis
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Definition: the division of the nucleus
Prophase:
chromatin coils up or condenses into visible double
chromosomes (two sister chromatids).
the nuclear envelope 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.
Cartoon version VS. real version (prophase)
Metaphase:
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the doubled chromosomes line up at the equator
(middle) of the cell moved by the spindle fibers attached
to their centromere.
Anaphase:
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the centromeres split separating the sister chromatids.
the spindle fibers pull the identical chromosomes towards
the opposite poles
Telophase: mainly the opposite of
prophase
Telophase:
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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: The division of Cytoplasm
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Animal cells: the plasma membrane pinches in along the
equator causing a furrow. The furrow deepens until the
cell is pinched in half.
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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.
cytokinesis