cell cycle

Question 1

checkpoints of cell cycle

Answer 1

G1/S
G2/M
SAC

Question 2

what does RB do

Answer 2

Retinoblastoma- tumour suppressor protein
unphophorylated form blocks E2F dependent transcription (E2F1, E2F2, E2F3) (eg of cyclin E)
therefore prevents cell cycle

Question 3

what phosphorylates RB proteins

Answer 3

cyclin D/ CDK4- allows progression in to cell cycle

Question 4

what does cdh1 form of APC/C do

Answer 4

degrade cyclin A (in G1 phase)

Question 5

what does cdc20 form of APC/C do

Answer 5

degrades cyclin B (allows segregation of DNA)

Question 6

what inhibitorily phosphorylates cyclin-CDK

Answer 6

Wee 1 kinase

Question 7

what unphosphorylates cyclin CDK

Answer 7

Cdc25 phosphotase

Question 8

what do p107 and p140 proteins do

Answer 8

allow transcription by inhibiting corepressors E2F4 and E2F5

Question 9

how does the cell ensure replication only occurs once

Answer 9

using opposing actions and switch mechanism of CDK2/cyclin A and APC/C-Cdh1 at G1/s phase
APC/Cdh1 degrades cyclin A and geminin in G1 phase
cyclin A/CDK2 and geminin inhibit DNA helicase loading and APC/Cdh1
step 1: helicase loading (licensing)
APCcdh1 inhibits cyclin A, allows helicase loading but inhibits replication and Cyclin A/CDK2
Step 2: activation of helicase and polymerase recruitment
cycA/CDK2 activates replication and inhibits helicase loading. Inhibits APC/cdh1

this switch allows loading of helicase in G1 and initiates replication at S

Question 10

G1 phase cyclin

Answer 10

E/ CDK2 (lasts during G1 only)

Question 11

S phase cyclin

Answer 11

cyclin A/CDK2

lasts through S phase and G2, decreases during M and increases during G1 phase (from beginning of cell cucle

Question 12

M phase cyclin

Answer 12

B/ CDK1

increases part way through G2 and lasts till Metaphase/anaphase boundary

Question 13

cyclin initating entry into G1 from G0

Answer 13

cyclin d/CDK4

Question 14

how are newly replicated chromosomes linked

Answer 14

topological linkage (topoisomerases resolve this)
chromosome cohesion (by COHESIN complex- ring formed with smc1 and smc3, closed by Scc1)

Question 15

what mediates cleavage of cohesin

Answer 15

SEPERASE

Question 16

seperase regulation

Answer 16

held in inactive state by CDK phosphorylation and by binding to securin inhibitor
activation of seperase by degradation of cyclin b and securin by APCcdc20

allows cleavage of cohesin ring, allowing chromosomes to sepeerate at metaphase
need tension for activation of seperasae

Question 17

centromere

Answer 17

region of chromosome that assembles kinetochore

Question 18

kinetochore

Answer 18

protein complex whichis point of attachment to MTs

Question 19

how is G2/M checkpoint activated

Answer 19

incomplete replication, DNA damage, ds breaks 
checkpoint kinases (ATM/ATR and Chk1 + 2) activate Wee1 kinase and repress Cdc phosphotase = inhibition of cyclin B and CDK1

Question 20

SAC regulates

Answer 20

prevents APC/Cdc20 activation until chromosomes correctly attached
mitotic checkpoint complex (MCC) binds and inhibits cdc 20 when kinetochores not attached and no tension

Question 21

cancer associated with high levels of which cyclin

Answer 21

cyclin e- chromosome overduplication

Question 22

what percentage of cancers are aneuploid

Answer 22

90%

Question 23

what does drug ribociclib do

Answer 23

inhibit cdk4 and cdk6 (others inhibit g2/m checkpoint kinases)

Question 24

centrosome

Answer 24

micrrotubule organising centre

Question 25

why do women become infertile with age

Answer 25

older oocytes = less ccohesin- cohesin of chromosome must last to last ovulation

Question 26

what cancers does egfr cause and drug treatment

Answer 26

pancreatic and Non smoking caused lung cancer

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