White: Cell cycle 1&2 Flashcards
Chromosomal duplication and segregation occur in which phase(s) of the cell cycle
Duplication- S phase
Segregation- M phase
G1 phase occurs between
M and S
G2 phase occurs between
S and M
Checkpoint I
START- cell commits to cell cycle entry and chromosome duplication
Checkpoint II
G2/M- Chromosome alignment on spindle in metaphase
Checkpoint III
Metaphase-to-anaphase - Trigger sister chromatid separation and cytokinesis
Cdk function
Phosphorylate proteins downstream to activate them and regulate cell cycle events
The cell cycle is governed by Cdks
Cyclins function
Proteins that regulate Cdks
Cdks must be bound to cyclin to be active and have protein kinase activity
Direct Cdks to their specific target
What is the variation in cyclin and Cdk levels throughout the cycle, if any?
Cyclin levels vary according to point of time in cell cycle, Cdk levels are constant
G1/S cyclins function
Start cell cycle Activate Cdks in late G1 Help trigger progression through start Commitment made to cell cycle entry Levels drop in S phase
S cyclins functions
Bind Cdks after progression through start
Help stimulate chromosome duplication
S-cyclin levels remain high until mitosis
M cyclins functions
Activate Cdks that stimulate entry into mitosis at G2/M checkpoint
Removed at about the middle of mitosis
CAK function
Cdk activating kinase
Phosphorylates Cdks to activate them
Wee1 Kinase
Inhibits Cdk activity by phosphorylating the “roof site” on Cdks
Cdc25
Phosphotase that dephosphorylates “roof site” to increase Cdk activity
CKI proteins
Cdk inhibitory proteins
Binds to both Cdk and cyclin to inactivate
SCF-ubiquitin ligase
Adds ubiquitin to CKIs to target for destruction
This activates the S-Cdks
SCF activity depends on
F-box subunit
M-Cdk is activated how
Cdc25 protein phosphatase removes inhibitory phosphates from M-Cdk
Progression from metaphase to anaphase is triggered by
Protein destruction, NOT PROTEIN PHOSPHORYLATION
APC/C
Anaphase-promoting complex
Catalyzes addition of ubiquitin to protein securin (which inhibits separase from cleaving cohesin)
Causes ubiquination of M-cyclins and S-cyclins
Activated by binding to Cdc20
Cohesin
Glues together sister chromatids along their length
Securin
Protects cohesin protein linkages that hold sister chromatid pairs together by inhibiting separase (an enzyme that cleaves cohesin)
PRE-RCs
Pre-replicative complexes
Assembly of PRE-RC is inhibited by Cdk activity
While S-Cdk and M-Cdk levels are high during S and M stage, NO PRE-RC is formed
Condensin
At the end of S phase, forms ring-like structures and uses ATP to promote compaction and resolution of sister chromatids (untangle them so they can be separated)
What triggers prophase, anaphase, prometaphase and metaphase
Increase of M-Cdk activity at G2/M
Kinetochore microtubules
Attach each chromosome to spindle pole
Interpolar microtubules
Hold two halves of spindle together
Astral microtubules
Interact with cell cortex
Dyneins
Minus-end directed motors
Link plus ends of astral microtubules to actin filaments at cell cortex
-By moving towards minus end of microtubule, the dynein motors pull the spindle poles away from eachother
Kinesin-5
Two motor domains that interact with plus ends of anti-parallel microtubules
Moves these two anti-parallel microtubules past each other to force the spindle poles apart
If there is no Kinesin-5, the spindle collapses
Kinesin-14
Minus-end directed motor, pulls poles together
Kinesin-4,10
Chromokinesins- plus-end directed motors
Push attached chromosomes away from the pole
Kinetochore
Responsible for attachment of spindle to chromosomes
There is an exposed open end for addition and removal of tubulin subunits from microtubules attached to kinetochore
Removal of tubulin subunits leads to force pulling kinetochore/chromosomes to pole of cell
3 Forces in chromosome movement
Depolymerization
Microtubule flux
Polar ejection force
Depolymerization
Depolymerization of the plus end of the microtubule drives the pulling of the kinetochore towards the pole
Microtubule flux
Tubulin added at plus end while being removed at minus end
-Occurs on interpolar microtubules
Polar ejection force
Kinesin-4,10 motors on chromosomes interact with microtubules and transport chromosomes from poles
Results in push-pull phenomenon
Anaphase A
Chromosomes move apart
-Due to spindle microtubule depolymerization at kinetochore
Anaphase B
Separation of spindle poles themselves
-By kinesin-5 motor proteins (also dynein pulls pole apart)
Mitogens
Stimulate cell division by triggering G1/S-Cdk activity
Survival factos
Suppress form of programmed cell dealth (apoptosis)
Mitogen Cell-cycle entry into S-phase
Mitogen binds receptor
Ras causes activation of MAP kinase cascade
Increase of gene regulatory proteins including Myc
Myc promotes entry into cell cycle by increasing expression of G1 cyclins
G1-Cdk-Cyclin activates gene regulatory factors called E2F proteins
E2F binds promotors of G1/S cyclin and S cyclin genes (leads to DNA transcription)
Rb protein
Tumor supressor protein
E2F protein is inhibited by interacting with Rb protein
Shuts down entry into S-phase
Active G1-Cdk phosphorylates Rb to reduce binding to E2F
What happens if Rb protein is inactive
No control going into cell cycle so cancer can occur (retinoblastoma)
ATM and ATR protein kinases
Activated by DNA damage
Phosphorylate Chk1 and Chk2 proteins
Chk1/2 proteins
Major target is p53 protein, which stimulates transcription of p21
p21 CKI
Binds to G1/S-Cdk and S-Cdk to inhibit activity (no cell division- damaged DNA must be repaired)
What if ATM/ATR proteins are not working
This can cause Ataxia telangiectasia and other cancers
Ras is mutated in __% of cancers, p53 is mutated in __% of cancers
Ras mutated in 30% of cancers
p53 mutated in 50% of cancers
PI-3 kinase pathway
Most important growth signaling pathway
PI-3 kinase adds ATP to inositol phospholipids
Activates TOR, which activates many factors for cell growth
