13. Eukaryotic cell cycle control Flashcards
the cell cycle is unidirectional, what does this mean?
proceeds in a set order - and never reverses
what happens in quiescence (G0)
cells remain dormant for months and even years
what do cell fusion experiments tell us
there must be a mitosis promoting factor in M phase cells
what stage cells respond to mitosis promoting factors
G1, G2, S phase
what stage cells are sensitive to S-phase promoting factor
G1 cells
why are Xenopus and sea urchin embryos frequently studied in cell cycle experiments
high protein content
what are the perks of studying Xenopus
frog cells produce lots of mRNA
what are the perks of studying sea urchins
large eggs that are easy to manipulate
what does MPF stand for
maturation promoting factor
what is the effect of progesterone
induces G2 arrested cells to mature and enter meiosis
what is the effect of adding hydroxyurea to cells in the cell cycle
arrests in S phase as it prevents DNA replication
adding cytoplasm from a cell nucleus arrested in meiosis II achieves what?
what does this show?
same thing as progesterone
- promotes meiosis
there is a soluble factor that can promote meiosis (MPD)
list the order of the cell cycle events
G1 phase
S phase
G2 phase
Mitotic phase
how long do drosophila cell divisions last during embryonic development
8 minutes
what happens once an egg is fertilised
high MPF activity keeps the egg arrested in metaphase of meiosis II
- fertilisation lowers MPF levels and meiosis is completed
how long are oocytes arrested in G2 for
why?
8 months
so they can grown and stockpile materials needed for multiple cleavages
what is a component of MPF
cyclin B
what is autoradiography
using a radioactive molecule we can assess whether it has been incorporated into a polypeptide
how was cyclin discovered
autoradiography using sea urchin eggs
radioactive methionine shows cyclin levels rise and fall (oscillate) following fertilisation
what is required for mitotic exit
degradation of cyclin B
why is Xenopus good to study
they produce large eggs
which are produced from synchronous cell cycles
what did frog oocyte experiments show
addition of sperm chromatin to oocyte cytoplasm enabled mitosis and spindle pole formation
as MPF was present in oocyte cytoplasm
what happens when RNase is added to sperm chromatin & oocyte cytoplasm
no longer undergoes mitosis and cyclin mRNA is destroyed
