The Cell Cycle
Day 3
Cancer: Out of Control Cell Division
• The defining feature of a cancerous cell is that
is divides much more often than is healthycreating 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
The Basics of Cell Division
• G1: Cell Growth, makes duplicate organelles,
increase in size
• S phase: Duplicates all the chromosomesphotocopying 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
http://www.daviddarling.info/encyclopedia/C/cell_cycle.html
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
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
Thinking like Cancer
• Which regulation point(s) would prevent
cancerous growth?
• What are a few ways cancerous cells could
bypass those points?
How do checkpoints work?
Hypothesis:
The cell cycle is directed by specific signaling
molecules present in the cytoplasm
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?
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
PDGF
Contact inhibition
• Normal cells form only a monolayer in culture
• Why?
Anchorage dependence
• Normal cells must have a surface on which to
grow or a tissue attachment to continue
replicating.
• Why?
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)
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 cell’s lifespan