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Dynamic Cell > regulation of 2nd cell cycle checkpoint > Flashcards

regulation of 2nd cell cycle checkpoint Flashcards

1
Q

S-Cdk activity enhances M-cyclin transcription

A

S-Cdk activates TFs

e.g. FoxM1

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2
Q

S-Cdk and FoxM1

A

S-Cdk phosphorylates FoxM1
-> allows PLK1 to bind

-> PLK1 phosphorylates FoxM1 at different location

  • > FoxM1 binds to DNA
  • > activates M-cyclin transcription
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3
Q

M-Cdk activity

- regulated by phosphorylation

A

cyclin binding to Cdk = partial activation of Cdk active site

phosphorylation fully activates
- initiated by CAK

Cdc25 phosphatase removes inhibitory Ps
= activated

Wee1 kinase adds inhibitory Ps
= inactive

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4
Q

what most happen to Cdc25 before it can dephosphorylate M-Cdk?

A

must be activated

- phosphorylated by PLK1

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5
Q

positive feedback of M-Cdk

A

active M-Cdk

  • > inhibits Wee1 kinase
  • > more active M-Cdk

active M-Cdk

  • > activates (+P) Cdc25
  • > more active M-Cdk
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6
Q

M-Cdk regulation due to subcellular localisation

A

M-Cdk first activated at centrosomes

then moves to nucleus in late Prophase

can only phosphorylate targets at these positions and these times

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7
Q

upstream regulators of M-Cdk at G2/M checkpoint

A

CAK

  • kinase activates M-Cdk
  • promotes cell cycle progression

Wee1

  • kinase inhibits M-Cdk
  • blocks

Cdc25

  • phosphatase activates M-Cdk as removes inhibitory phosphates
  • promotes

M-Cdk

  • kinase (+ve feedback on own activation)
  • promotes
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8
Q

how is G1/S-Cdk inactivated?

A

ubiquitination

E1 + E2 + E3 enzymes work together to add ubiquitin

  • > tags G1/S-cyclin for degradation at proteasome
  • > no activity of G1/S-Cdk
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9
Q

SCF complex

- what is it?

A

E3 ubiquitin ligase

contains an F-box protein
- gives specificity of protein degradation

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10
Q

incomplete DNA replication triggers..?

A

DNA damage response

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11
Q

incomplete DNA replication

- process

A
  1. stalled replication fork
  2. ATR kinase activated
  3. Chk1 kinase activated
  4. phosphorylates p53 (unbinds
    Mdm2) = active
  5. p53 binds to p21 regulatory region
  6. p21 transcribed and translated
  7. p21 binds and inhibits active M-Cdk
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12
Q

how is the incomplete DNA replication checkpoint block further upregulated?

A

Chk1 kinase

  • > inhibits Cdc25
  • > cannot remove inhibitory Ps from M-Cdk
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13
Q

incomplete DNA replication mediated regulators of G1/S-Cdk and S-Cdk at Start checkpoint

A

ATR + Chk1

  • kinases
  • block

Mdm2

  • ubiquitin ligase
  • promotes

p53

  • TF
  • blocks

p21

  • inactivates cyclin-Cdks
  • blocks
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14
Q

how does DNA damage prevent G1/S-Cdk + S-Cdk activation?

A
  1. DNA damage
  2. activates ATM kinase
  3. activates Chk2 kinase
  4. phosphorylates p53
  5. activates p21 transcription
  6. p21 inhibits G1/S-Cdk and S-Cdk via binding
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15
Q

DNA damage mediated regulators of G1/S-Cdk + S-Cdk at Start checkpoint

A

ATM and Chk2

  • kinases
  • block

Mdm2

  • ubiquitin ligase
  • promotes

p53

  • TF
  • block

p21

  • cyclin-Cdk inhibitor
  • block
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16
Q

how does M-Cdk promote entry into mitosis?

A 
4 key changes in early mitosis:
> NMBD
> centrosome separation 
> formation + stabilisation of MTs
> chromosome condensation
17
Q

M-Cdk activates 2 protein kinase families

A

Polo-like kinases (Plk)
-> assembly of mitotic spindles,
removal of cohesions,
centrosome maturation

Aurora kinases (e.g. Aurora-A)
-> assembly + stabilisation of mitotic spindle,
spindle attachment to sister chromatids

= mitosis

18
Q

condensin

A

5-subunit protein

uses energy from ATP hydrolysis to rearrange chromatin structure
-> condensation

19
Q

nuclear pore subunits + nuclear lamins

A

phosphorylation
initiates disassembly of nuclear pore complexes + nuclear lamins
away from the nuclear envelope

20
Q

kinesin 5

A

phosphorylation of kinesin-5 motor proteins by M-CDk + Aurora-A kinase

-> drives them to separate the centrosomes

21
Q

TACC

A

MT-associated protein

phosphorylated by M-Cdk
-> stabilises MTs

22
Q

regulators of entry into mitosis

A

M-Cdk

  • kinase
  • promotes

Plk

  • kinase
  • promotes

Aurora-A + Aurora-B

  • kinases
  • promotes

Dynamic Cell (15 decks)

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