WEEK 12 (Apoptosis) Flashcards
Which processes determine organ and body size?
- Cell growth
- Cell division
- Cell death
What is Apoptosis?
A neat orderly process characterised by the overall shrinkage in volume of the cell and its nucleus, the loss of adhesion to neighbouring cells, formation of blebs at the cell surface, dissection of chromatin into small fragments and rapid engulfment of “corpse” by phagocytosis
What is necrosis characterised by?
- Swelling of both the cell and its internal membranous organelles
- Membrane breakdown
- Leakage of cell contents into the medium
- Resulting induction of inflammation.
What do both apoptosis and necrosis have in common?
Both can occur as a regulated and programmed process
What differentiates apoptosis from necrosis?
CELL NECROSIS = cells swell and burst, spilling their contents all over their neighbours
CELL APOPTOSIS = die quickly and cleanly without damaging its neighbours
What does the rapid removal of the dying cell in apoptosis allow for?
- Avoids the damaging consequences of cell necrosis
- Allows organic components of the apoptotic cell to be recycled by the cell that ingests it
What is the difference between the Intrinsic pathway and the Extrinsic pathway of Apoptosis?
INTRINSIC PATHWAY = Internal stimuli trigger apoptosis by the intrinsic pathway
EXTRINSIC PATHWAY = Signal to commit suicide comes from a neighbouring cell
What are caspases?
The molecular machinery responsible for apoptosis and are activated in response to signals that induce apoptosis
What are the two types of Caspases?
- INITIATOR CASPASES = cleave and activate downstream executioner caspases
- EXECUTIONER CASPASES = activate additional executioners, kicking off an amplifying, proteolytic cascade and others dismember other key proteins in the cell
What are the properties of the Caspase cascade?
- Destructive
- Self-amplifying
- Irreversible
What are the main proteins that regulate the activation of caspases?
BAX & BAK
[Bax and Bak are death-promoting members of the Bcl2 family]
What happens when Bak or Bax are activated by an apoptotic stimulus?
It AGGREGATES in the outer mitochondrial membrane leading to the release of CYTOCHROME C into the cytosol -> CYTOCHROME C binds to an adaptor and assembles into a seven-armed complex (binds with PROCASPASE-9 to form an APOPTOSOME) -> PROCASPASE-9 becomes activated within the apoptosome and now activates different procaspases in the cytosol -> CASPASE CASCADE and APOPTOSIS
Which specific initiator procaspase does Deathinducing signalling complex (DISc) include?
Procaspase 8 or 10
How do some extracellular signals activate cell death in a neighbouring cell?
- Affecting the activity of members of the Bcl2 family of proteins
- Activating a set of cell-surface receptor proteins called “death receptors”
How does the death receptor “Fas” work?
Fas is activated by a membrane-bound protein called “FAS LIGAND” present on the surface of specialised immune cells called killer lymphocytes