apoptosis and cellular senescence Flashcards
who coined the word apoptosis
wyllie and currie who worked on tumour histopathology un edinbrugh
what is necrosis
cell death following injury, infection it provokes the immune response while apoptosis does not.
name markers for apoptosis
-cell morphology
-DNA ladders
-tunel assay: label termini DNA fragments with fluorescent group by enzyme terminal transferase.
-binding of annexin v to cells. this is caused by membrane changes and is assayed in flow cytometer.
-activation by caspase enzymes which is followed by assaying by western blotting.
name the 3 stages of apoptosis and what is involved in each one
decision: survival factors, TNF,Fas, Bcl-2 family, p53, DNA damage
execution: caspases, nucleases, surface modifications.
death: phagocytosis.
how are caspases expressed
as pro enzymes which require activation
what are the 3 domains in a caspase
N-terminal, large, small
how are caspases activated by proteolytic cleavage between domains
the large and small subunit form heterodimers. the activation site between large and small domains is a caspase recognition site. this results in a caspase cascade
what is the result of caspases being very specific
they recognise and degrade very few proteins. it is highly effective.
what do initiator caspases do
activate a cascade resulting in activation of executioner caspases
how are caspases 8 and 10 activated
by death receptors via FADD
how is caspase 9 activated
by APAF-1, cytochrome C, and ATP via the caspase recruitment domain. initiated by intracellular events such as p53
what do caspase 7 and 3 do
induce cell killing
how do caspase inhibitors work
bind to catalytic site of caspases.
what does c-FLIP (flice inhibitory protein) do
inhibits caspase 8. over expression of this protein is common in tumours resistant to death inducing signals such as TRIAL
describe the function of FADD
recruited from the cytoplasm. binds through death domain cluster. it acts as a adapter protein. it also has a death effector domain. binds molecules like caspase 8 and 10. causes activation of initiation of apoptosis.
hoe do death receptors signal death
bind to cytotoxic lignads
what mechanism prevent external death signals
soluble decoy receptors, membrane bound decoy receptors, intracellular signalling activators and inhibitors.
how is death receptor activated
ligand binding, receptor trimerization, intracellular death domain cluster signals pro-apoptotic signal
what are the BCL-2 family and where are they found and what is there structure
anti-apoptotic, in B cell lymphocytes, 25-26 Kda membrane protein.
name some homologues of BCL-2
BAX, forms heterodimers with bcl-2 and inactivates bcl-2
name the classes of the bcl-2 family proteins and examples for each one
anti-apoptotic BCL-2 :bcl-2, bcl-XL
pro-apoptotic BH123: Bax, Bak
pro-apoptotic BH-3 only: Bad, Bim, Bid, Puma, Noxa.
what is PUMA
p53 upregulated modulator of apoptosis.
in the intrinsic pathway how is cytochrome C released
the BH123 proteins aggregate and act as the apoptotic stimulus
what protein prevents the BH123 proteins from coming together
the active anti-apoptotic Bcl-2 protein
