lec 19 cell death Flashcards
3 ways a cell can die
necrosis
apoptosis
autophagy
how is necrosis induced
by insults to the cell that cannot be repaired
e.g. injury, infection, cancer, infarction
outline the process of necrosis
cell swells
chromatin gets digested
organelle membranes get disrupted
cell lyses and spills contents into surrounding area
hydrolytic enzymes can damage neighbouring cells
inflammation caused and potential of gangrene
why is apoptosis so important - what is it required for?
developing mammalian foetus - producing individual digits for hands and feet
tadpole-frog development - tail cells die by apoptosis
quality control - non0functional or misplaced cells must eb removed
T and B cells develop to produce a population where only the specific antigen recognition is allowed
balance: cell division = cell death
outline the process of apoptosis
cells shrink
cytoskeleton collapses
golgi fragments
NE disassembles
chromatin hyper-condenses and is digested
cell membrane blebs into apoptotic bodies
cell membrane chemically altered so it is recognised by neighbouring cells and macrophages
cell membrane permeavle to small molecules
regulation of apoptosis
a specific class of proteases with a Cys residue in their actve site
they cleave targets at an Asp residue
‘C-Asp-ases’
cleavage leads directly to activation
the extrinsic cascade - apoptosis
extracellular signalling proteins e.g. TNF and Fas can bind to TM proteins (death receptors)
lipid raft fusion and clustering of death receptors - death domain
DISC (death inducing signalling complex) recruited
apoptosis initiated
cortical actin ring
required for apoptotic blebbing
assembly brought about by Caspase cleavage of Rho-Kinase (ROCK)
contracts using Myosin-II
intermediate filaments and microtubules in apoptosis
IFs e.g. cytokeratin are cleaved by Caspase
MTs are dismantled early but re-appear later as extensive arrays
possibly due to modifications of tubulin
