Cell Cycle Control System
Cyclical set of molecules that triggers and coordinates main events in the eukaryotic cell cycle. It makes sure events occur only once, at proper times, and in the correct order.
Point where stop and go-ahead signals monitor process of cell cycle
(Signal trandsuction pathways launches the signals)
3 Major Checkpoints
(These checkpoints correspond to the 3 phases in the cell cycle)
What does the G1 Checkpoint check?
1. Cell Size
2. Genetic Material
If the genetic material is NOT damaged. If it is damaged, then the process is delayed and the genetic material is repaired. If there is a stop signal, the cell exits and enters G0.
State in which cells leave the cell cycle and do NOT divide
(Most cells in our bodies are in the G0 phase)
What does the G2 Checkpoint check?
1. Genetic Material Duplication
2. Cell Size
3. Genetic Material Completeness
If damage is detected, chromosomes are repaired
What does the M Checkpoint check?
1. Genetic Material Attachment
If all chromosomes are attached to spindle fibers from both poles
External physical factors that effect cell division
1. Growth Factors
2. Density-dependent Inhibition
3. Anchorage Dependence
Proteins received in the plasma membrane that stimulate cells to divide
Contact with other cells causes an animal cell to stop dividing
Requirement that a cell must be attached to a substratum, such as the inside of a culture flask, in order for the cell to divide
Cancer cells do not respond to signals that trigger checkpoints in the control system; thus, they grow and divide rapidly. Density-dependent inhibition and anchorage dependence do not effect cancer cells.
(Cancer is a disease of the cell cycle.)
Proteins that advance cells past checkpoints and through the cycle.
Kinases that phosphorylate other proteins
Activate Cdks and help control progression from one stage of the cell cycle to the next. After the cell passes a checkpoint, the cyclins are destroyed, and specific new cyclins for the next checkpoint emerge.