Cell Cycle 2

Question 1

how is the metaphase-anaphase tansition triggered

Answer 1

by regulated proteolysis

Question 2

what are S-CDK and M-CDK complexes regulatroy targets of

Answer 2

the anaphase promoting complex or cyclosome (APC/C)

Question 3

how does APC/C trigger cells to go through mitosis

Answer 3

anaphase promoting complex act by ubiquitin groups covelantly to cyclins- this is then degraded by proteosome

Question 4

what is APC/C and why does it target proteins

Answer 4

ubiquitin ligase and targets for degredation by proteosome

Question 5

describe 3 features of APC/C

Answer 5

small
covalently attached
ubiquitin covalently attched to lysin side chain on target protein

Question 6

how are polyubiquitin chains formed

Answer 6

by linking additional ubiquitin chains by Lys48

Question 7

how is degradation by proteosomes triggered

Answer 7

by adding more ubiquitin to create long chains

Question 8

what are the 3 different domains of ubiquitin

Answer 8

unfoldase ring
central cyclinder-protease
cap

Question 9

how is APC/C activated

Answer 9

Cdc20 activates in mid-mitosis

Cdh1 activates from late mitosis to G1

Question 10

what happens when s and m-cdk activity is abolished

Answer 10

proteins previously phosphorylated in s phase to early mitosis need to be dephosphorylated before mitosis and cytokinesis can be completed

Question 11

how do you get out of mitosos

Answer 11

must remove phophates essentially reversing effect of protein kinases

Question 12

what is securin

Answer 12

the second major target of APC/C in mitosis

Question 13

what does securin do

Answer 13

acts by inhibiting activity of protease called seperase

Question 14

what happens when securin is degraded

Answer 14

at the end of metaphase by APC/C this frees seperase to cleave one of the subunits of a protein complex called cohesion

Question 15

what happens when there is a loss of cohesion

Answer 15

result in sister chromatid seperation in anaphase

Question 16

how does separase break cohesion complex

Answer 16

breaks ring keeping chromatids together

Question 17

describe the contrasting roles of cyclin cdk and apc/c

Answer 17

cyclin-cdk activity drives cell cycle progression

apc/c action triggers chromosome segregation

Question 18

what is SCF

Answer 18

another ubiquitin ligase but one that functions in s phase

Question 19

what does SCF do

Answer 19

targets various CKIs for destruction in late G1 and is responsible for G1/S cyclin destruction in early S phase

Question 20

compare APC/C and SPF

Answer 20

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

Question 21

why is S-CDK activity required

Answer 21

for initiation of chromosome replication

Question 22

how is replication initiation triggered

Answer 22

by increase in s-cdk activity

Question 23

what is activated at each stage of cycle

Answer 23

s pahse= scdk
mphase= mcdk
g1= apc/c and cdk inactivation

Question 24

what do s-cdk phosphorylate

Answer 24

two proteins Sld2 and Sld3 and this facilitates assembly of CMG complex

Question 25

what drives entry into mitosis

Answer 25

psotive feedback loop causes sharp increase in M-CDK activity

Question 26

what triggers cytokinesis events

Answer 26

APC/C destruction of securin and cyc;ins

Question 27

how is APC/C sister chromatin seperaration achievde

Answer 27

by securin degradation resulting in activation of seperase which cleaves cohesion to open cohesion ring

Question 28

what happens if one chromosome fails to align on spindle

Answer 28

unattached chromsome kinetichore binds to Mad2 protien which undergoes conformational change to inhibit cdc20-APC/C