1.5c Control of the cell cycle Flashcards
Progression of cell cycle.
The progression of the cell cycle is controlled by checkpoints.
Checkpoints
Checkpoints are mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met.
G1 - cell growth
M - chromosomal attachment
G2 - cell damage
Cyclin proteins
Cyclin proteins that accumulate during cell growth are involved in regulating the cell cycle.
Cyclins combine with and activate cyclin-dependant kinases (CDKs). Active cyclin-CDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs
G1 checkpoint
At the G1 checkpoint, retinoblastoma (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.
Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb). This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.
G2 checkpoint
At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed. DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.
Metaphase checkpoint
A metaphase checkpoint controls progression from metaphase to anaphase. At this checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.
Uncontrolled reduction/increase in rate of cell cycle
An uncontrolled reduction in the rate of the cell cycle may result in degenerative disease.
An uncontrolled increase in the rate of the cell cycle may result in tumour formation.
Proto-oncogene
A proto-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene.
