cell death Flashcards
necrosis =
uncontrolled large scale cell death
apoptosis =
programmed cell death (self suicide of 50 billion cells per day)
what are the physical causes of necrosis?
trauma, cuts, burns, extreme temps (e.g. frostbite → cellular fluid freezes)
what type of toxins cause necrosis?
internal = bacterial toxins, external = snake venom
how does acute hypoxia/ischaemia cause necrosis?
stroke → tissues die from deprived blood flow → no O2
describe the process of reversible necrosis
ATP dependent pumps stop working due to lack of O2 → so ion conc increases → water moves into cell by osmosis
membrane integrity compromised from cell and organelle swelling
describe irreversible necrosis
cellular calcium level too high → autolysis occurs (destruction of cells by own enzymes especially is lysosome bursts) → cell lysis (breaking membrane down) → inflammatory response activated
describe the process of apoptosis
cell shrinkage → DNA fragmentation and nuclear breakdown → breakdown of cytoskeleton → formation of apoptotic bodies → phagocytosis of apoptotic bodies
(no inflammatory response)
why can’t apoptosis occur in ischaemic conditions?
requires O2
what is apoptosis’ relationship with autophagy?
if lots of organelle death occurs in 1 cell it will be phagocytosed
describe the physiological situations where apoptosis occurs
→ tissue size maintenance
→ developmental cell loss
→ removal of immune cells after immune response
→ hormone → menstruation
describe the pathological situations where apoptosis occurs
→ DNA damage (by radiation, oxidation, stress) in own cell nucleus
→ induced in virally infected cells to prevent spread of virus
give 4 examples of developmental apoptosis
C.elegans nematode worm:
→ 1mm long with 1100 cells → 131 die during development
metamorphic in tadpoles:
→ surge in thyroid hormone → initiates apoptosis in tail cells → results in adult frog
digit formation in mice:
→ web cells are apoptosis by releaser of local signalling proteins
refinement of neural connections:
→ apoptosis adjusts no. of neuronal cells to size of target by competition for survival factors
give an event where both necrosis and apoptosis are involved
brain ischaemia:
→ cells in middle → site of O2 starvation → die through necrosis
→ cells around edge → die through apoptosis → prevents the spread of cell death
model for studying apoptotic pathways =
C.elegans
Ced genes are involved in ________________ leading to engulfment of _______ via ________
recognition of apoptotic signals, apoptotic cells, phagocytosis
describe the basic pathway of Ced genes
IL-1 → CED-9 → CED-4 → CED-3 → apoptosis
which CED genes are pro-apoptotic?
IL-1, CED-4, CED-3
which CED gene is anti-apoptotic?
CED-9
______ are executioners of cell death and essential for apoptosis
caspases
EGL-1 =
CED-9 =
CED-4 =
CED-3 =
BH3
BCL2
APAF1
caspases
what are the 2 pathways for the activation of apoptosis?
intrinsic and extrinsic
describe the extrinsic pathway for activation of apoptosis
→ tumour necrosis factor family (TNF)
→ 6 related death receptors in trimmers on cell surface
apoptotic signal → Fas ligand on killer lymphocyte (CD4+) binds to death receptor → activation of caspase 8 → death inducing signalling cascade activated
describe the intrinsic pathway for activation of apoptosis
takes place inside the cell being apoptosed
triggered by DNA damage → release of mitochondrial contents or developmental signals
