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Ch. 17 - Cell Cycle Part 2 A summary of the chapter and lecture notes on the cell cycle, part 2. Includes illustrations and graphics from the textbook.

Course Code
BIOL 2021
Julie Clark

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BIOL 2021- May 5 2009
- Everything depends on M-CDK activation
- M-CDK activation causes all early events in mitosis
Activation of M-CDK
1) Increase m cyclin gene expression
Leads to M-cyclin levels
- CDK activating kinase (CAK) puts on an activating phosphate
- Wee 1 kinase inactivates
All that needs to be done is remove inactivating phosphate to become active
2) Activation of cdc 25 phosphatase
Removes inhibitory phosphate
- Mcdk inhibiting wee 1
- Mcdk activates cdc25
All or nothing switch
- Cdc 25 activation : don’t know what activates it

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Figure: condensin
M-CDK phosphorylates proteins
Assemble of mitotic spindle
Phosphorylates proteins that cause the breakdown of nuclear envelop (Lamins)
Rearrrangements of actin cytoskeleton and Golgi
Phosphorylates proteins that cause chromosome condensation
- Proteins called condensing condenses chromosomes and winds up DNA (above).
MCDK phosphorylates condensin and activates it
- Bipolar array of microtubules
Minus end at poles
- 3 kinds of microtubules with different roles:
1) Interpolar: between the poles
Anti-parallel in the middle
2) Kinetochore
Attached to sister chromatids at kinetochore
3) Astral
Outward from centrosome

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Go to cell cortex
Not found in all cells
- G1/S-CDK triggers centrosome
- Centrosome duplication (beginning of S phase)
- At beginning of M phase (mitosis), mcdk is activated which causes formation of spindle
Mcdk phosphorylates MAP, microtubules become shorter and more dynamic
Phosphorylation of centrosome
GAMMA TUBULIN RING COMPLEX (increased nucleation)
- Gets put/created in centrosome causing more microtubules to form
- M cdk phosphorylates motor proteins
- Dyneins go to minus end
Pull tubules toward cortex
Centrosomes move apart
- Kinesin 5: plus end directing
Pushes poles apart (2 feet attach to different microtubules)
- * Kinesin 14: minus end directing
Pulls poles together
- Need a balance of opposing forces
- Kinesin 4,10: to plus end
Attached to chromosomes and carry them to plus end of microtubules which is where they
need to be at metaphase
- Attach chromosomes to kinetochore
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