regulating cell division and specialization Flashcards
what are checkpoints
they monitor when a cell should begin dividing and when to proceed into next phase
what controls entry to the next checkpoints
cell signaling controls entry
what major events must go correctly and carefully
1) entry into mitosis
2) chromosomal segregation
3) cytokinesis
what are the 4 general phases of the cell cycle
1) G1 -> cell growth/size increase
2) S-Phase -> synthesis/ duplicate DNA
3) G2 Phase-> prepare for division (enzymes and metabolic changes)
4) M-Phase -> mitosis and cytokineses
what is unique about cell cycles in mutlicellaur organisms
cell division occurs at different rates
( embryo:20 minutes , Skin Cells: 12-24 hours), liver: 1 every 1-2 years)
what type of cells don’t divide once mature
nerve and muscle cells
what is coordinated between different tissues in cell divion
rates and timing
what is the G1 checkpoint and what does it control
checkpoint before entering S-Phase
1) controlled by growth factors
2)checks to see DNA is good (not damaged)
3) determines whether cell can enter S-Phase
what is the G2 checkpoint and what does it control?
checkpoint before entering mitosis
1) checks to see if DNA is replicated properly
2) determines whether a cell can enter mitosis
what is the M checkpoint and what does it control
checkpoint after mitosis
1) checks to see if the spindle fiber attachment on chromosomes are correct -> allows for proper separation of chromosomes
what provides stop and go chemical signals at checkpoints
internal and external signals like activators and inhibitors
what are some internal signals
-promoting factors -> cant do mitosis unless all of DNA is replicated
what are some external signals
growth factors-> stimulate mitosis in wounded cells
what are some examples of external cues
1) density dependent inhibition -> crowded cells stop growing
2) anchorage dependence -> cells don’t divide unless anchored to something (basement membrane)
What is one specific example of external cues
1) cells anchor to the dish surface to divide (anchorage)
2) cells stop dividing, once a SINGLE layer of cells has been made ( density-dependent inhibition)
3) if some cells are scraped away, the remaining cells will divide to cover up the once full of cell spot (density-dependent inhibition)
what are cyclins
families of proteins that regulate the timing of the cell cycle -> constantly made and broken down
what do cyclin-dependent kinases or CDK do
they add a phosphate group to activate other enzymes in certain phases of the cell cycle.
What does a Cyclin and CDk Complex do?
they allow cells to move across checkpoints in each phase
what is important about Cyclin and CDK involving evolution
they are evolutionarily conserved -> a core conserved process unifying all living things
what is a G0 phase
a non dividing stage where a cell might exit into
what happens if a cell doesn’t receive a signal
it can exit the cell cycle and go into G0
what are some examples of cells in G0 phase
- liver cells are called out of G0 by external cues
-muscle and nerve cells always go into G0-> don’t divide
what is cancer
a mutation in DNA that controls the cell cycle
what are some mutations that can lead to cancer
1) molecular switches to divide turned on all the time
2) programmed cell death (apoptosis) doesn’t happen
what are some cancer mutations caused by
UV radiation, chemical exposure, radiation, pollution, smoke, age,genetics, viruses
what is the p53 gene
a gene that stops the cell cycle at G1 checkpoints by triggering CDK inhibitors
what does the p53 gene do?
-activated enzymes that repair DNA
-trigger apoptosis if DNA cant be repaired
stopes cells at G1 checkpoints
what is important about p53
it is the single most mutated gene in cancer
