Cell Cycle Flashcards
prophase
DNA disentangled and condensed
metaphase
chromosomes line up at equator
anaphase
separation of chromosomes
telophase
chromosomes packed into new nuclei
cytokinesis
cytoplasm division
Interphase
G1 + S + G2
Metaphase
mitosis and cytokinesis
G1 phase
most cells are here! most cells have 2n chromosomes (4n after replication)
in dividing cells
G0 phase
quiescent cells - not dividing but can be stimulated to divide (enter cell cycle) if enough nutrients etc
post-mitotic cells
incapable of cell divisions
i.e. neurons - made synaptic connections - lost when cell divides
R checkpoint
right before G1/S - beginning cell replication
enter cell cycle and leave G0
is environment favorable?
don’t want to divide if the cells can’t grow
once pass R check pt - have to finish unless catastrophe
cells check GROWTH conditions before commiting - before: how much GF signalling is there? after: doesn’t matter
NOT G1/S
only unexpected disasters can stop
stays in G0 if not enough extracelular signals to proceed through R
G2/M checkpoint
before cells enter mitosis
is environment favorable?
is all DNA replicated?
crisis?
metaphase to anaphase checkpoint
trigger anaphase and proceed to cytokinsesis
are all chromosomes attached to the spindle?
CDKs
inactive unless bound to cyclin
cyclin dependent kinase
activated to start and inactivated to stop
regulated by transcription, phosphorylation, protein degredation
G1(R)-CDK
Cyclin D, CDK4 and CDK6
G1-S CDK
Cyclin E, CDK2
S-CDK
Cyclin A, CDK2 and CDK1
G2/M-CDK
Cyclin B, CDK1
Cyclin-CDK inhibitors
p27, p21 - binds to cyclin cdk and inactivates it
i.e. if UV DNA damage - p53 (tumor suppressor) is activated –> nucleus –> transcribes p21 –> binds to G1/S CDK and S-CDK - inactivates it
CDK phosphorylation
to signal completion of S phase!
if fails - premature M entry - cell has too much DNA
During S:
wee1 phosphorylates and inhibits CDK1 activity
at G2/M:
Cdc25 removes phosphatases and activates cdk1
Cyclin levels oscillation
how do cells progress through the R phase?
cyclin D!
Wnt/beta catenin stimulate cyclin D transcription
APC blocks Wnt - if no APC - a lot of Wnt - lots of growth and deregulation (colon cancer)
other growth signals affect transcription of Cyclin D
Progression from Cyclin D to Cyclin E
from R phase to G1/S phase
E2F is transcription factor for Cyclin E
pRB - bound to E2F so it’s supporessed
Cyclin D is activated by GF –> phosphorylate Rb –> Rb drops E2F –> E2F goes into nucleus to stim Cyclin E synthesis
initiates DNA replication
if mutation in Rb –> cells always entering cell cycle even if not ready
Cyclin E - how does it trigger?
prereplicative complexes put on DNA in G1
Cyclin E - phosphorylates complexes so they are degraded! - preinitiation can bind and synthesis can occur -
don’t want more than 1 round of DNA synthesis
triggers DNA replication activity
DNA syn can’t be triggered after S phase because prereplicative complexes are gone
ubiquitin system
E1, E2, E3
E1 - uses ATP to make a high E bond, ubiquitin activating enzyme, E1 + ATP binds to upiquitin
E2- ubiquitin carrier, E1 transferes activated ubiquitin, conjugation protein
E3 - E2 complexes with E3, recognizes which proteins need ubiquitin - puts ubiquitin on it - repeats until there is a chain and rounds it up in proteosome - degrades
if no E1 - stops cell cycle
SFC complex
multisubunit ubiquitin ligase
Skp, Cul, F-box
F-box = specificity - interchangeable, belongs to specific target proteins and brings them close to E2 for ubiquitin tag
Rbx = E2
F-box - mostly degrades phosphoproteins, cyclins and CDKs phosphorylate
allows substrates to be degraded at specific phases (i.e. Cyclin E is degraded!)
APC - Anaphase Promoting Complex
E3 ubiquitin ligase
targets cell cycle proteins for degredation via ubiquitin by proteosome
triggers transition from metaphase to anaphase by triggering proteins for degredation
CDC20 - activates APC + ubiquitin + E2 and E3, polyubiquitination chain on G2/M cyclin (cyclin B) -degrade in proteasome!
ALSO:
cohesin holds chromosomes together - activated APC cleaves securin from separase - separace can cleave cohesin and allow the chromosomes to separate
Growth Factor signalling affects?
Cyclin D
Degredation by proteasome affects?
Cyclin E (ubiquitin), Cyclin B (apc/ubiquitin)
also sep chromosomes in Mphase
characteristics of apoptosis
active - proteins are made
cells shrink - use E
intact membrane
nuclear condensation
phagocytosis of cell corpse
characteristics of necrosis
passive! damaged
cells swell
membranes rupture
inflammatory response
TUNEL
mark to see where DNA is fragmenting
casparases
executioners of apoptosis
cystein in the active site but cut at D (aspartic acid)
active only when cells need to die
cascade - 1 molecule of active initiator caspacse cuts a ton of proteins including executioner caspases
CAD
DNAase
ICAD - inhibits CAD and is normally bound - ICAD is cleaved by effector caspase and CAD can cleave DNA
extrinisic pway
apoptosis triggered from the outside
Fas ligand - binds to Fas death receptor - Fas R trimerize –> Fadd adaptor proteins bind –> procaspases bind –> initator caspases cut each other and gain activity –> cut self to increase activity and cut executioners for cascade
caspase 8
used in intrinsic pway
form DISC complex w FADD adaptor proteins and Fas death receptor
intrinic pathway
mitochondria –> release cytochrome c from intermembrane space –> activates Apaf1 and hydrolysis of ATP to ADP –> conf change –> all bind together to form apoptosome –> recruit procaspase 9 –> acleave and activate and cleave executioner procaspases
caspase 9
caspase activated by intrinsic pway
Bcl2
4 BH domains - 1, 2, 3, 4
anti-apoptosis
regulates cytochrome c release
oncogene - prevents cells from dying!
BH123
pro-apoptotic - 3 BH domains
BH3-only protein
pro-apoptotic - when activated - inhibits Blc-2 (antiapoptotic) an tips balance toward apoptosis
BH123 protein aggregate and make a pore so mitochondria proteins leave
ABT737
Bcl-2 inhibitor
potential anti-cancer drug
acts like BH3-only!
Bcl-2 is increased in cancer cells - keeps them alive, ABT looks like BH-3 and neutralizes Bcl2 which allows cells to die
IAP
inhibitor of apoptosis proteins - bind to caspaces to inactivate
tumor - increased IAP! blocks cell death - bind and block unnecesary caspase activation
anti-IAP - blocks IAP so cells can die
Smac
IAP antagonist
IAPs binding to caspases to inhibit apoptosis
Smac inactivates IAPs so there is apoptosis!
cancer treatments
p53 and apoptosis
p53 can induce BH3 only protein transcriptions –> apoptosis
summary of extrinsic apoptotic pway
summary of intrinsic apoptotic pway
TNF alpha
hits TNF receptor –> death domain –> caspases –> apoptosis OR
kinase signalling pway –> necrosis –> recruits alarmins and immune cells (inflammation)
viruses have many ways to avoid apoptosis! body does necrosis and recruitsimmune cells
induced by infection!
MLKL
pseudokinase
kinase signalling pway induced by TNFalpha
inserts into membrane and punctures holes so membrane ruptures- TNFalpha induced necrosis
