Regulation of Cell Division Flashcards
to replicat
late g1-s cyclins transcribed
s cyclin binds to cdk-s/cdk/cyclin complex
late g1-pre-rc compelx-orc , cdcbound, mcm (recruted by cdc binding to orc)
s/cdk/cyclin phosphorylases cdkb+ORC
cdcb phosphortalted and degraded
mcm able to act as helices, exits nucleus
DNA pol+machinery recruited
cdcb and mcm leave
-cdcb phosphorylated through g2
go back to this after slides
Internal vs external controls
internal-monitors cell cycle progression, make sure occur in step wise succession
external-stimultate cell division when more cells needed-block when they are not
use of g1/g2
what parts are part of interphase
time delay for cells to grow-accumulate mass
time delay for monitoring intra/extra cellular conditions
G1, g2, and s
Restriction point
what if not favorable
@ end of G1-measures favorability of environemnt
- passes restribction point and is COMMITTED TO DNA REP
- cant go back if go past this point even if conditions are unfavorable
enter g0
important features of cell cycle control (4)
certain time to turn on specific event
initate events in correct order
make sure each event is only triggered 1x per cell cycle
on/off switches-trigger events in complete/reversible style
what happens when enter s, m, leave m
trigger DNA rep machinery
trigger mitosis machinery
trigger cytokinesis
cyclin depedent kinase
CDK
activity increases/decreases at different stages of cell cycle
leads to phosphorylation of different proteins at different times in cell cycle-inittates/regs key events
Dependnt on cyclins for kinase activity
Different cyclins for different parts of cell cycle
mCDK vs sCDK
spindle assembly + other mitosis machinery turns on
enzymes for replication are phosphorylated (activated)
4 classes of cdks + associated cyclin
g1-promtes passage through restriction point -cyclin D g1/s-commits cell to replication -cyclin E s-intitates replication -cyclin A m-promotes mitosis -cyclin B
molecular swtich
cyclin/cdk-initiate different steps of cell cycle
- poised for activation
- recieve signal to become fully activated (usually phosphorylation)
how ensure switches fire in correct order/fire once per cycle?
feedback mechanisms
S-cdk control + function
controls initiation of DNA replication once per cell cycle at replication origins
Origins of replication-origins of replication-large multi-protein complex binds here
s cyclin transcribed in late g1
s-cdk activated-phosphorylates cdc6_preRC
-point of no return
ORC
binds throughout cell and acts as landing pads for other reg proteins-initiate replication at different positions throughout the genome
binds early g1
pre replicative complex
cdc6 and orc
Mcm comes in (helices)
-together with all 3-posited to go if environemnt favorable
Phosphorylation of Cdc6
phosphorylation of orc
degradation
by s-cdk
fucking draw slide 24
How is invitiation of entry to S phase controlled (3 parts)
CDC6
- usually present at low levels throughout cell cycle-but increasingly transiently in early g1
- binds to ORC-causes recruitment of Mcm protein which are helices
- ORC, CDC6, MCM make pre-RC-poised to replicate DNA
s-cdk
- iniitated by expression of s-cyclin
- phosphorylation
- assembles DNA polymerase and other replication machinery at the origins
- activate the mcm proteins to slide along the DNA and act as helices
- phosphorylates mcm proteins and causes thier export from the nucleus
- upon completion-no cdc6 and no mcm
S cyclin
- origin is now ready to fire-requires activity of S-CDK
- S-cyclin transcription is activated in late G1
- S cdk inactive without s-cyclin present
- s cyclin -cdk complex forms activating s-cdk that then phosphorylates pre-RC activating it for replication
- does this by degrading cdc6 in pre-RC
- complex then can recruit poly _other machinery+allow mcm to do helices activity
S cdk prevents re-replication
Phosphorylation of cdc6 by S-cdk causes cdc6 to dissocatite from ORC-after origen fired for replication
-disassembly of pec-prevents replication from occurring at same origin
Dissocatio nand phophrylation of Cdc6 from ORC causes its degradation
S-cdk phosphorylates Mcm/helicase proteins and cause their export from nucleus
draw slide 28
ways to prevent re-replication
S-cdk activity remains high in G2 and mitosis causes Cdc6 protein to be always phosphorylated and therefore prevents re-replication
M-cdk-phosphorylat]es Cdc6 and MCM
How does cell cycle control system reset itself to allow replication
At end mitosis -Cdk activity is reduced to zero
- no CDK to phosphoryylate Cdc6+CM
- new Cdc6+mcm made in net cell cycle-wont be phosphorylated
results in dephosphorylted Cdc6 and MCM proteins allowing pre-RC assembly to occur again
Triggering entry to mitosis (3 proteins)
Activation of M cyclin
Have a system tha is poised and ready to go
M cyclin-gradually increases during G2 and M phases
CAK-Cdk activating Kinase
Wee1-Cdk inhibitory kinase
draw slide 31
CAK
Cyclin activates CDK conformational change to expose active t-loop
CAK comes in and phosphorylates t-loop
Wee1
CDK activating phosphate
-Wee1 adds another phosphate-inhibits
- poised for activation-just need to take off inhibitory phosphate
- done by cdc25
M-cdk
phosphorylates proteins that are responsible for assembly of simple, chromasome condensation, breakdown of nuclear envelope
Feedback of M-cdk
M-cdk inhibits Wee1 causing more activated M-cdk to form
M cdk phosphorylates more cdc25 activting more phosphatase that leads to more actived m-cdk
Inactivation of m-cdk
allows for exit of mitosis
APC+Cdc20-creates active APC
- CATALYYZED BY M-CDK - add ubiquitin to M-clyclin-degredation in proteasome
G1 phase is characterized by+mechanisms to ensure this
absence of Cdk activity =ubiquitin mediated degradation of sdks =cyclin kinase inhibitor accumulation =decreased cyclin transcription -mediated by retinoblastoma protein and E2F transcription factor
why is there not cdi in g1
increased cki activity (p27), and increased rb
p27 (or 21…?)`
a ck. that bind and inactivates active cyclin-cdk complex
-expression stimulated by p53
decreased cyclin transcription is caused by
Rb protein
E2F is a TF that regulates expression of many genes required for entry into s phase including G1-S and S cyclins
- controlled in part by Rb protein
- during G1, Rb binds to E2F and blocks its activity
- results in downstream genes (G1/S and S cyclins) not being transcribed
When cells receive an extra-cellular signal to divide, G1-Cdk accumulates, phosphorylates Rb, and reduces affinity of Rb to E2F which results in expression G1/S and S cyclins
Retinoblastoma-Less than two copies of Rb gene
DRAW 42/44
Rb feedback loops
EfF is released by Rb inactivation, E2F then increases its own expression
E2F expression leads to production of G1/S-cdk and S-cdk
-phosphorylates more Rb and released E2F
Increase on G1/CDK and S-CDk activities enhances the phosphorylation of ubiquitin ligases and CKIs, leading to thier destruction i nproteosome and as a consequence activate G1/s-Cdk and S cdk
DNA checkpoints
late g1 and late g2
g2 checkpoint
DNA damaged in late g2 before mito
Damaged DNA send signal that blocks cdc25 activity
cdc25 removes inhibitory phosphate put on by wee1
p53 and g1 dna damage checkpoint
g1 prevents progression into S by inhibiting activation of g1/scdk and s cdk complexes
-controlled partially by p53
p53 stimulates expression of several gens including CKI protein (p21)
