16. Regulation Of The Cell Cyle In G2,M

Question 1

Timing when MPF is activated by Cdc25

Answer 1

1. Once DNA has been entirely doubled

2. Cell size is appropriate

Question 2

two positive feedback effect of the active MPF

Answer 2

1. Further stimulation of Cdc25
2. Suppression of Wee 1
   * it increases cyclin B level from G2 to metaphase
   And decreases till anaphase(; degraded MPF) by APC(Anaphase Promoting complex; Ub ligase) and this is for prevention from premature separation

Question 3

Six effects of MPF

Answer 3

1. Condensin(S phase ring structure) ->chromatin condensation
2. Lamin phosphorylated -> removing nuclear envelope
3. GM130 reponsible for Golgi and ER division
4. Microtubule protein forming mitotic spindle
5. Myosin light chain (MLC) preventing from immature cytokinesis
6. APC degrading MPF, and also securin (consequentially, cohesin is degraded and sister chromatid seperates)
   * all effects from prophase to metaphase

Question 4

Mechanism of disintegration of nuclear envelope

Answer 4

Lamin filament is separated into Lamin dimer by MPF (Cdk 1- Cyclin B complex)

Question 5

Mechanism of Cohesin degradation (=overcoming mitotic spindle checkpoint)

Answer 5

1. Before microtubules not attached to kinetochores, Kinetochore has Mad and Bub keep subunits of APC with it ; inhibiting APC essentially
2. Once microtubule attache to kinetochores, Mad and Bub finally releases APC subunits and APC forms the complex and induced by MPF
3. APC separates cyclin B from the MPF complex and securin(separase inhibitor) and cyclin B and securin are ubiquitinated and degraded by proteasome
4. Free separase degrades cohesin and now two sister chromatids are free for separation (Anaphase starts) by pulling spindle microtubules