BIOL408, Unit 4- M-phase/cell division

what was the significance of xenopus cytoplasm in discovering cell cycle regulation?

there were stopping points found between cell cycle phases, when cytoplasm from meiosis II cells were inserted into cells in G2, there were no stops indicating there was something present in the cytoplasm regulating activity

what was the significance of the cell cycles in sea urchins?

they found that expression of a certain protein (cyclins) were synonymous with a certain phase of the cell cycle

MPF

cyclin/CDK complex for M-phase, M-cyclin and Cdc2

Cdc2

CDK for M-phase, regulates cell division

how is Cdc2 activated?

it binds to M-cyclin, which allows it to be phosphorylated

what two molecules regulate Cdc2 activation?

Wee1 and Cdc25

where does phosphorylation occur on Cdc2?

T14/Y15, blocks the activation site

what are three substrates the MPF phosphorylates to regulate M-phase?

nuclear filaments/lamins, microtubule associated proteins (MAP), and anaphase promoting complex (APC)

what happens when MPF phosphorylates nuclear filaments?

it leads to the breakdown of the nuclear envelope during prophase/prometaphase

what happens when MPF phosphorylates MAP?

leads to microtubule reorganization so that spindles can form

what happens when MPF phosphorylates APC?

targets M-cyclin for degradation to stop the cell from dividing again

APC

ubiquitinator protein, helps regulate cell division by degrading m-CDK and cleaves cohesion proteins that hold chromosomes together

Sec1

cohesion proteins that keep sister chromatids attached

separase

cleaves Scc1

securin

binds to separase to prevent cleavage of cohesion proteins until it is time for division

how does APC regulate sister chromatid division?

when phosphorylated, it ubiquitinates securin, activating separase

G2 checkpoint

DNA damage checkpoint before cell enters M-phase

what happens when DNA damage is detected at the G2 checkpoint?

cdc25 is inhibited, which prevents M-CDK activity and division

M-checkpoint

checks to make sure there is proper spindle attachment at the centromere

Mad2

protein that inhibits APC by binding to unattached kinetochores to prevent premature chromosome separation