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.
- plasma membrane becomes more permeable
- cell swells and the membrane ruptures
- release of proteases leading to dissolution and auto-digestion of the cell
- 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
- (phosphatidylserine lipid appears in outer leaflet) - Chromatin and nuclear condensation
- DNA fragmentation
- Formation of membrane blebs`(bulge/protrusion)
- 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)
2. 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 PCD - some, but not all, features of apoptosis
- Necrosis-like PCD - “Aborted apoptosis”
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
-carry out apoptosis
Which caspases are initiator caspases?
2, 8, 9 and 10
- trigger apoptosis
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 (p20 and p10) 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 large and 2 small chains to form an active L2S2 heterotetramer
What are the two mechanisms of caspase activation?
- Death by design (receptor-mediated extrinsic)
2. Death by default (mitochondrial (intrinsic) death pathway)
Describe the structure of death receptors.
consist of:
- Cysteine-rich extracellular domain
- Transmembrane domain
- Intracellular tail with a death domain (DD)
What are the two important adaptor proteins in the death by design pathway (extrinsic) and how are they different?
1.FADD – positive regulator that promotes cell death
– FADD= DED (death effector domain) + DD (death domain)
2. FLIP – negative regulator that inhibits the death pathway and allows regulation
- FLIP = DED + DED