apoptosis Flashcards
why do we need programmed cell death *
remove harmful cells eg cells with a viral infection/dna damage
developmentally defective cells eg B lymphoscyetes expressing Ab against self-ag
excess/unnecessary cells - embryonic development ie in brain to eliminate excess neurons, liver regeneration, sculpting digits (apoptosis of the membrane between the digits) and organogenesis
obsolete cells - eg mammary epithelium is apoptosed at end of lactation to return the breast to the normal size
exploitation - used in chemo - induce apoptosis to reduce number of tumour cells
what is the TUNEL technique
labels apoptopic cells
what is necrosis *
unregulated cell death associated with trauma cellular disruption and an inflammatory response
what is apoptosis *
programmed cell death
regulated cell death, controlled disassembly of cellular contents without diruption - no inflammatory response
it is stimulated and timely
describe pathway of necrosis *
the plasma membrane becomes permeable
water enters = cells swell = rupture of cell membranes = everything is deregulated because it is not contained in the plasma membrane
chromatin condenses
dissolution of cellular structure - degregation of organelles
lysis
release of proteases leading to autodigestion and dissolution of the cell
phagocytes clean the debris
causes localised inflamm because proteins are at sites that they shouldnt be
neighbouring cells proliferate and fill the gap
what is the pathway of apoptosis *
can be localised - ie only 1 cell effected
latent phase
- death pathways are activated (molecular changes) but cells appear morphologically the same
execution phase
- loss of microvilli and intracellular junctions (comprimise the permeability of a cell)
- cell shrinkage
- loss of plasma mem asymmetry (normally membrane at top of cell is differnet from that at bottom etc ie phosphatidylserine lipid appears in outer leaflet of the lipid bilayer, normally only on inside)
- chromatin and nuclear condensation
- DNA fragmentation
- surrounding epi close around the apoptotic cell - restores permeability
- formation of membrane blebs
- fragmentation into membrane enclosed apoptopic bodies
- apoptotic boduies are phagocytosed by neighbouring cells and and reving macrophages
plasma membrane remains intact - therefore no inflammation because there is no release of contents out of the cell
SEM of apoptotic bodies *
dark areas are the apoptotic bodies - being taken up by macrophages
describe DNA modification in apoptosis, and how it can be seen *
DNA ladders - fragmentation - separate the DNA based on size in agarose gel
at 0 mins the DNA is intact - bulky and too large to go into the gel - the is DNA condensation but no freagmentation in the nucleus
at 45mins - intact DNA disappears and can see ladder of fragmented DNA
this is increased at 70 mins - blebs of DNA
using TUNEL assay - the flurescence labels fragments of DNA - cells that have flurescened nuclei are apoptotic - those that dont are not
what are the 4 main types of cell death and explain them *
necrosis - unregulated cell eath associated with cellular disruption ad an inflammatory response
apoptosis - programmed cell death (PCD) - regulated, controlled disassembly of cellular contents, no inflammation
apoptosis-like PCD - some but not all features of apoptosis, display phagocytic recognition molecules before plasma membrane lysis
necrosis-like PCD - variable features of apoptosis before cell lysis - called aborted apoptosis
is there a graded response of cell death *
yes - apoptosis at one end and necrosis at other
many differnet types in middle
apoptosis requires ATP, necrosis doesnt
what are the mechanisms of apoptotic cell death *
the executioners - caspases
initiating the death program via death receptors/mt - sequential actions of proteins leading to steps in cell
the Bcl-3 family
stopping the death program
what are caspases *
Cysteine-dependant ASPartate-directed proteASES
they are proteases with specific cysteine and aspartate recognition sites
they are the excutioners of apoptosis
need to be tightly regulated - they are present in inactive form(auto-folded on itself or as dimers) and are activated by proteolysis
describe the structure of initiator caspases, what are the 4 initiator caspases *
they are caspase 2, 9, 10 and 8
they have homogous domains
2 and 9 have CARD - CAspase Recruitment Domain - this domain places the caspases at a specific subsite in a cell
all have p20 and p10 domains
caspase 10 and 8 have DED domains - Death Effector Domains
10 and 8 undergo homotypic protein-protein interactions ie 8 binds to 8
describe the structure of effector caspases, what are the effector caspases *
they are caspase 3 6 7
they have p20 and p10 domains
describe caspase maturation *
caspases are synthesised as procaspases/zymogens - have prodomain and LS and SS domains
prodomain is cleaved and procaspase is activated by dimerisation
SS domain is also cleaved - so only LS domains are involved in dimerisation (ie a light and heavy subunit are left)
the folding of 2 large adn 2 small chains forms an active L2S2 heterotetramer
eg heterodimerisation of capsase 8 and 3 - therefore they are close together so can synchronise the following steps
