signals which induce somatic cell division Flashcards
what are destinies of cell
G0: To remain alive and functioning without dividing
To grow and divide
Cell death (apoptosis)
what are Cyclin dependent kinases
and what controls cell destiny
The signals regulating these processes are an intense area of research
Cyclin dependent kinases (Cdk’s) regulate the initiation of cell growth
They are switched on and off by cyclins (their levels rise & fall in the cell cycle)
Extracellular compounds are the key regulators of these processes
what are cell cycle checkpoints?
Cell cycle checkpoints are control mechanisms that ensure the reliability of cell division
These checkpoints verify whether the processes at each phase of the cell cycle have been accurately completed before progression into the next phase.
what do cell cycle check point check for
checkpoints assess DNA damage, which is detected by sensor mechanisms.
what occurs when damage is detected at cell cycle checkpoint?
When damage is found, the checkpoint uses a signal mechanism either to stall the cell cycle until repairs are made or, if repairs cannot be made, to target the cell for destruction via apoptosis
what checkpoint is found at G1 phase and what does it do?
There is a phase late in G1 phase called the restriction point (RP, or the restriction checkpoint); cells that should cease division exit the cell cycle and enter G0.
what cells overcome RP.
Cells that continually divide in the adult human include hematopoietic stem cells and gut epithelial cells. Their re-entrant into the cell cycle is possible only by overcoming the RP.
how is RP overcome
This is achieved by growth factor-induced expression of cyclin D proteins. These then overcome the G0 barrier and are able to enter the cell cycle
what occurs in growth hormone-induced or oncogenic-induced progression
In growth hormone-induced or oncogenic-induced progression, cyclin D expression increases. Increased expression of cyclin D allows its interaction with CDK4.
how is transcription factor E2F inhibition relived
interaction of CDK4 and cyclin D causes activation of CDK4-cyclin D
Once active CDK4-cyclin D complexes form, they phosphorylate the tumor suppressor (growth inhibitor) retinoblastoma protein (Rb), which relieves the inhibition of the transcription factor E2F.
what does E2F do?
E2F is then able to cause expression of proteins needed for cell growth eg cyclin E.
where is the second checkpoint located?
The second checkpoint is located at the end of G2 phase, triggering the start of the M phase
where does mitotic spindle checkpoint occur
The mitotic spindle checkpoint occurs at the point in metaphase where all the chromosomes should have aligned at the mitotic plate and be under bipolar tension.
how is anaphase initiated?
The tension created by the bipolar attachment in metaphase is sensed, which initiates the anaphase entry
what is a check point ?
A checkpoint is one of several points in the eukaryotic cell cycle at which the progression of a cell to the next stage in the cycle can be halted until conditions are favorable.
