The Cell Cycle

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The Cell Cycle

• Day 3

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Cancer Out of Control Cell Division

• The defining feature of a cancerous cell is that
  is divides much more often than is healthy-
  creating a stack of cells called a tumor
• How does it do that? It has to bypass all the
  checkpoints that tell it to stop dividing

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The Basics of Cell Division

• G1 Cell Growth, makes duplicate organelles,
  increase in size
• S phase Duplicates all the chromosomes-
  photocopying of information
• G2 More growth, time needed to gain strength for
  mitosis
• Mitosis- Cell divides up the chromosomes so each
  of the new daughter cells has all the information
• Cytokinesis- The cell breaks into two cells

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ycle.html
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Key Regulation Points

• G1 check point before S phase (DNA replication)
  can start, pass if
• Nutrients sufficient
• Growth factors present- there is a need for more
  cells
• Cell is big enough
• DNA is undamaged

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Key Regulation Points

• G2 check point before Mitosis
• Chromosome replication completed
• No DNA damage
• Active signals to start mitosis (chemicals in the
  cytoplasm)
• Metaphase check point before cell splits
• All chromosomes are aligned to be equally passed
  down to the new cells

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Thinking like Cancer

• Which regulation point(s) would prevent cancerous
  growth?
• What are a few ways cancerous cells could bypass
  those points?

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How do checkpoints work?

• Hypothesis
• The cell cycle is directed by specific signaling
  molecules present in the cytoplasm

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How would you design an experiment to test this
hypothesis?

• Materials
• Cells in culture
• Any measurement device
• Think about
• What data are relevant?
• How long will your experiment take?

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What do we know so far?

• Still working out all the chemical and physical
  signals.
• Over 50 growth factors have been identified
• Different cell types respond differently to
  different growth factors

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PDGF
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Contact inhibition

• Normal cells form only a monolayer in culture
• Why?

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Anchorage dependence

• Normal cells must have a surface on which to grow
  or a tissue attachment to continue replicating.
• Why?

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Telomeres- fingerprints of cancer

• Cancer often has specific characteristics related
  to too much division
• Each time the cell divides it replicates its
  chromosomes- increasing the chance for mutation
  and shortening the telomere (the end of the
  chromosome)

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Discovery of telomerase

• Telomerase re-lengthens the chromosome to enable
  division to continue
• Cancer cells have to increase telomerase activity
  so that they do not die
• This is a key regulation step of a cells
  lifespan