Transcript Cell Cycle Regulation

Cell Cycle Regulation
Cell Cycle analogy to washer machine control
The cell cycle is driven by an internal clock regulated at certain
checkpoints by both external (ex: faucets) and internal (ex:
sensor) controls.
Major Checkpoints of the Cell Cycle Control System
Cell Cycle Clock: Cyclins and CyclinDependent Kinases
Cyclin fluctuates cyclically within the
cell.
Cyclin–dependent kinases (Cdks) such
as MPF must be attached to cyclin to be
active (MPF = mitosis promoting factor)
Activity of Cdks rise and fall with
changes in cyclin concentration.
MPF complex initiates mitosis by
phosphorylating a variety of proteins.
MPF switches itself off by initiating a
process that breaks down cyclin.
The effect of a Growth Factor
on Cell Division
PDGF = plateletderived growth factor
A growth factor is a protein released by certain body cells
that stimulates other cells to divide.
Density-Dependent Inhibition
• Crowded cells stop dividing.
• Cultured cells normally divide
until they form a monolayer.
• If some cells are removed, cell
division begins in cells bordering
the gap until it is filled.
• Most animal cells also exhibit
anchorage dependence
Cancer cells have escaped from cell
cycle controls
Cancer cells:
• do not exhibit density-dependent inhibition or
anchorage dependence.
• do not stop dividing when growth factors are
depleted.
• can go on dividing indefinitely in culture if
given a continual supply of nutrients (immortal).
• transformation is the process that converts
a normal cell to a cancer cell.