Apoptosis Flashcards
Define Necrosis.
Unregulated cell death associated with trauma, cellular disruption and an inflammatory response
Define Apoptosis.
Regulated cell death; controlled disassembly of cellular contents without disruption – no inflammatory response
Describe the process of necrosis.
The plasma membrane becomes more permeable – the cell swells and the membrane ruptures
Proteases are released leading to dissolution and autodigestion of thecell
There is localised inflammation
What are the two phases of apoptosis? Describe them.
Latent phase
Death pathways are activated, but cells appear morphologically the same
Execution phase:
Loss of microvilli and intercellular junctions
Cell shrinkage
Loss of plasma membrane asymmetry
Chromatin and nuclear condensation
DNA fragmentation
Formation of membrane blebs
Fragmentation into membrane enclose apoptotic bodies (these are then taken up by macrophages)
What is an important feature of apoptosis that distinguishes itfrom necrosis?
Plasma membrane remains intact – no inflammation
What DNA modification is seen during apoptosis?
Fragmentation of DNA ladders (seen in agarose gel)
Formation of more ends, which are labelled by adding an extra fluorescently-labelled tag in a TUNEL assay
What other types of cell death are there other than necrosis and apoptosis?
Apoptosis-like cell death
Necrosis-like cell death (sort of like an aborted apoptosis that ends up being necrosis)
NOTE: cell death is GRADED
What are caspases?
Cysteine-dependent aspartate-directed proteases
They are the executioners of apoptosis
They are activated by cleavage
Which caspases are effector caspases?
3, 6 and 7
Which caspases are initiator caspases?
2, 8, 9 and 10
Describe the structure of effector caspases.
They are single chain polypeptides consisting of a small and large subunit
The subunits are released by proteolytic cleavage
Describe the structure of initiator caspases.
They have the same two subunits found in effector caspases but they also have a targeting subunit (protein-protein interacting domain)
What are the two types of targeting subunit that initiator caspases can have?
CARD – caspase recruitment domain
DED – death effector domain
How are active caspases formed?
Cleavage of inactive procaspases is followed by the folding of 2 largeand 2 small chains to form an active L2S2 heterotetramer
What are the two mechanisms of apoptosis
Death by design (receptor-mediated)
Death by default (mitochondrial (intrinsic) death pathway)
Describe the structure of death receptors.
Cysteine-rich extracellular domain
Transmembrane domain
Intracellular tail with a death domain (DD)