Cell cycle

Question 1

Activation of MPF

Answer 1

• CDK
• Cyclin
• Phosphorylation of the complex

Question 2

Cyclin dependent kinase inhibitor CKI

Answer 2

• interacts with cyclin CDK complex⇒ inhibit kinase activity

- usually in response to environmental signal or damaged DNA ⇒ p53 ⇒ p21 ⇒ inhibition of G1/S CDK cyclin complex

Question 3

Wee kinase

Answer 3

• can add an inhibitory phosphate to CDK1 ⇒ inactivation

Question 4

INK CKI

Answer 4

• CDK inhibitor

- inhibits cyclin D with CDK4 and CDK6 in G1 phase

Question 5

KIP/CIP CKI

Answer 5

• CDK ihibitor

- inhibits cyclin E with CDK2 in G1/S phase

Question 6

G1 phase

Answer 6

• Components: Cyclin D + CDK4 + CDK6
• Phsophorylates retinoblstom Rb
• it detaches from E2F ⇒ G1/S transition is possible

Question 7

G1/S phase

Answer 7

• Components: Cyclin E + CDK2
• form a complex in late G1
• cyclin E rapidly degraded and released CDK2 forms complex with cyclin A
• this sequence is necessary for the initiation of DNA synthesis in S phase

Question 8

S phase

Answer 8

• Components: Cyclin A + CDK2 + CDK1

Question 9

M phase

Answer 9

• Components: Cyclin B + CDK1
• transition from G2 ti M
• phsophorylates:
  
  • nuclear lamines
  • chromatin condensation
  • cytoskeletal rearrangement
  • APC activation

Question 10

ATM

Answer 10

• protein kinase that is associated with genome
• if DNA contain double-stranded break, the resulting change in the conformation of the chromatin activates ATM
• upon activation ⇒ 1 subunit of activated ATM dimer dissociates + initiates cascade if protein phosphorylation-dephosphorylation events mediated by CHK1 and CHK2 protein kinases

Question 11

CHK1/2

Answer 11

phosphorylation of cdc25 (inactivation)

Question 12

Cdc25

Answer 12

• Phosphatase

- Removes inhibitory phosphate from CDK

Question 13

p53

Answer 13

• gene when activated by CHK ⇒ activates transcription of p21 + other proteins which cause cell apoptosis

Question 14

p21

Answer 14

• potent CDK-cyclin inhibitor that can efficiently inhibit the action of all CDKs ⇒ cell cycle stopped to allow time for extensively damaged DNA to be repaired

Question 15

APC

Answer 15

• E3 ubiquitin ligase
• marks target cell cycle proteins for degradation in the proteasome
• main function is to trigger the transition from metaphase to anaphase by tagging specific proteins for degradation
• also target mitotic cyclins for degradation ⇒ inactivation of G2/M CDK-cyclin complex ⇒ end of mitosis and cytokinesis
• marks for degradation the anaphase inhibitor, and CDK1 and cyclin B

Question 16

Cell cycle Check points

Answer 16

• G2/M:
  
  • entering mitosis
  • is DNA good and replicated
  • is environment favorable
• Metaphase ⇒ anaphase:
  
  • are all chromosomes attached to mitotic spindle
• G1/S:
  
  • entering the cell cycle
  • is the environment favorable