I' Cell Division

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I. Cell Division

• precise replication of DNA

• In mitosis separation of DNA into two identical
  daughter cells

• In bacteria (prokaryotes) called binary fission
  (asexual)

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II. The Cell Cycle

• alternates between

M Phase dividing phase
Interphase nondividing phase
M Phase ? shortest phase

• Mitosis

• Cytokinesis

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Interphase ? 90 of cell cycle growth and
metabolic activities
G1 phase ? 1st growth phase
S phase ? synthesis phase when DNA is synthesized
and chromosomes are replicated
G2 ? second growth phase
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Seen in G2
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MITOSIS
Prophase
Prometaphase
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Metaphase
Anaphase
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Telophase
Cytokinesis
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III. Cytokinesis
Plant Cells ? cell plate
Animal Cells ? cleavage
Exception
SLIME MOLDS
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IV. Cell Division Requirements

• Essential nutrients

• Ability to do protein synthesis (no poisons)

• PDGF (platelet derived growth factor)

• Density dependent inhibition

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• Restriction Points

• occurs late in G1

• if the cell is destined to divide, it progresses
  past the restriction point into the S phase

• if the cell is NOT destined to divide, it exits
  the cell cycle and enters the Go phase

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• most cells in the body are in the Go phase

Nerve and muscle cells may stay in Go permanently
In actively dividing cells, amount of cytoplasm
is the most important indicator of whether or not
a cell will pass the restriction point.
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• MPF (maturation promoting factor)

CDC2 transition from interphase to M phase
Cyclin triggers activation of proteins to cause
mitosis
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V. Cancer Cells

• do not exhibit density-dependent inhibition

• do not pay attention to the restriction point

• cancer cells are immortal if nutrients are
  available

ARE TRANSFORMED