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,• Proteins within the cell control the cell cycle
– Signals affecting critical checkpoints determine
whether the cell will divide (cyclins, kinases)
G1 checkpoint
Control
system
M checkpoint G2 checkpoint Figure 8.9A
, Anchorage, cell density, and chemical growth
factors affect cell division
• In laboratory cultures, normal cells divide only
when attached to a surface
= anchorage dependent
, • Cells continue dividing until they touch one
another
= density-dependent inhibition
Cells anchor to dish surface and
divide.
When cells have formed a
complete single layer, they stop
dividing (density-dependent
inhibition).
If some cells are scraped away,
the remaining cells divide to fill
the dish with a single layer and
then stop (density-dependent
inhibition).
Figure 8.8A