Cell Cycle 2 Flashcards
how is the metaphase-anaphase tansition triggered
by regulated proteolysis
what are S-CDK and M-CDK complexes regulatroy targets of
the anaphase promoting complex or cyclosome (APC/C)
how does APC/C trigger cells to go through mitosis
anaphase promoting complex act by ubiquitin groups covelantly to cyclins- this is then degraded by proteosome
what is APC/C and why does it target proteins
ubiquitin ligase and targets for degredation by proteosome
describe 3 features of APC/C
small
covalently attached
ubiquitin covalently attched to lysin side chain on target protein
how are polyubiquitin chains formed
by linking additional ubiquitin chains by Lys48
how is degradation by proteosomes triggered
by adding more ubiquitin to create long chains
what are the 3 different domains of ubiquitin
unfoldase ring
central cyclinder-protease
cap
how is APC/C activated
Cdc20 activates in mid-mitosis
Cdh1 activates from late mitosis to G1
what happens when s and m-cdk activity is abolished
proteins previously phosphorylated in s phase to early mitosis need to be dephosphorylated before mitosis and cytokinesis can be completed
how do you get out of mitosos
must remove phophates essentially reversing effect of protein kinases
what is securin
the second major target of APC/C in mitosis
what does securin do
acts by inhibiting activity of protease called seperase
what happens when securin is degraded
at the end of metaphase by APC/C this frees seperase to cleave one of the subunits of a protein complex called cohesion
what happens when there is a loss of cohesion
result in sister chromatid seperation in anaphase
how does separase break cohesion complex
breaks ring keeping chromatids together
describe the contrasting roles of cyclin cdk and apc/c
cyclin-cdk activity drives cell cycle progression
apc/c action triggers chromosome segregation
what is SCF
another ubiquitin ligase but one that functions in s phase
what does SCF do
targets various CKIs for destruction in late G1 and is responsible for G1/S cyclin destruction in early S phase
compare APC/C and SPF
functions mid mitosis to G1
15 subunits
requires actiavtion by Cdc20 and Cdh1
functions in G1-S transition
5 subunits
always present by requires substaret to be phosphorylates
why is S-CDK activity required
for initiation of chromosome replication
how is replication initiation triggered
by increase in s-cdk activity
what is activated at each stage of cycle
s pahse= scdk
mphase= mcdk
g1= apc/c and cdk inactivation
what do s-cdk phosphorylate
two proteins Sld2 and Sld3 and this facilitates assembly of CMG complex
what drives entry into mitosis
psotive feedback loop causes sharp increase in M-CDK activity
what triggers cytokinesis events
APC/C destruction of securin and cyc;ins
how is APC/C sister chromatin seperaration achievde
by securin degradation resulting in activation of seperase which cleaves cohesion to open cohesion ring
what happens if one chromosome fails to align on spindle
unattached chromsome kinetichore binds to Mad2 protien which undergoes conformational change to inhibit cdc20-APC/C
