Cell Cycle

Question 1

Entry to Cell Cycle

Answer 1

Mitogenic signals (eg. growth factors) releases CDK4/6 from inhibition by INK4 proteins (p15, p16)

Question 2

G1 phase

Answer 2

CyclinD-CDK4/6 promote SEQUESTERS CyclinE-CDK2 inhibitors (CIP-KIP proteins (eg. p21 p27)

PHOSPHORYLATION of RB inactivates it - releases E2F TF, induces CycE-CDK2, hyperphosphorylates RB, positive feedback, drives G1-S transition

Question 3

S phase

Answer 3

CyclinA-CDK2

Question 4

G2 phase

Answer 4

CycA-CDK1

Question 5

Mitosis

Answer 5

PLK activates phosphatase CDC25 which dephosphorylates and activates CycB-CDK1

PLK1 induces phosphorylation-dependent degradation of WEE1
CycB-CDK1 promotes CDC25 activity and WEE1 inhibition (positive feedback)

Question 6

G1/S Checkpoint,

G2/M Checkpoint

Answer 6

ATR/ATM kinase phosphorylates and activates CHK1/2, phosphorylates and activates p53 which activate p21 (CIP-KIP), inhibiting CycE-CDK2

ATR/ATM kinase –> CHK1/CHK2 phosphorylation and activation
Phosphorylates and inactivates CDC25
Phosphorylates and activates p53 –> p21 –> Arrest