PAUSE - CELL CYCLE 4

Question 1

what do abnormally high levels of Myc cause?

Answer 1

activation of p19ARF, which binds and inhibits Mdm2 and thereby causes increase levels of p53
depending on cell type and extracellular conditions p53 can cause cell cycle arrest or apoptosis

Question 2

what happens to cells that are forced to express telomerase?

Answer 2

have more cell divisions than normal cells
can even become immortal
their telomeres also become longer

Question 3

what do growth factors do?

Answer 3

signals for the cell to grow in size
activation of PI 3-kinase, which promotes protein synthesis through the activation of eIF4E and S6 kinase
growth factors also inhibit protein breakdown

Question 4

how is cell death used to match the number of developing nerve cells to the number of target cells they contact?

Answer 4

more nerve cells are produced that can be supported by the limited of survival factors released by the target cells
some cells dont get enough survival factors, undergo apoptosis
strategy to control overproduction

Question 5

what are the two ways in which survival factors prevent apoptosis?

Answer 5

1. binding of survival factor to the cell surface receptor leads to activation of various protein kinases (PKB)
2. PKB phosphorylates and inactivates the protein Bad
3. when inactive, Bad dissociated from Bcl-2 to suppress apoptosis
4. PKB phosphorylates and inhibits gene regulatory proteins
5. these proteins encode proteins that promote apoptosis

Question 6

what happens in the confluent monolayer?

Answer 6

cells no longer proliferate
no space
no more mitogens

Question 7

what do cells need to undergo cell division (in terms of physical constraints)?

Answer 7

need anchorage
cells that were spread on a large adhesive patch went into S phase more readily that cells suspended in agar or on a small patch