CP2: Cell death Flashcards
(15 cards)
What is apoptosis?
Programmed cell death (once the process is started, it is irreversible)
What is necrosis?
Cell death due to excessive stress/acute injury.
What is the purpose of apoptosis?
Control cell numbers, remove potentially harmful cells, prevent pathogen replication by removing infected cells.
What is the process of apoptosis?
1) Pyknosis: irreversible & irregular condensation of DNA.
2) Karyohexis: fragmentation of nuclear DNA.
3) Membrane gets blebs & apoptotic fragments are released.
What is the process of necrosis?
1) Excessive stress/injury leads to rapid energy depletion & metabolic disturbance.
2) Ionic gradient collapses.
3) Membrane loses its integrity.
4) Cell swells until it bursts & releases its macromolecules.
Define caspase.
Enzyme that regulates apoptosis.
How do caspases regulate the apoptotic cascade?
Initiator caspase is very specific & starts the apoptotic cascade.
Executioner caspases catalyses the cleavage of proteins to kill cell (enzyme is not very specific so many proteins are targeted).
How can apoptosis be regulated, apart from caspases?
Anti-apoptotic proteins prevent the unwanted release of cytochrome C.
What are the 2 apoptotic pathways?
Intrinsic & extrinsic
What happens in the intrinsic apoptotic pathway?
1) Mitochondria is disturbed & releases cytochrome C.
2) Cytochrome C gather proteins & forms the apoptosome.
3) Apoptosome activates caspase 9.
4) Executioner caspases 3 & 7 are activated and cleave lots of proteins, fragment DNA, disturb the nuclear enveloppe & cell cytoskeleton & cleave cell adhesins.
What happens in the extrinsic apoptotic pathway?
1) Fas-L & TNF bind to the death receptor,
2) Death receptor gathers proteins to form a DISC complex.
3) DISC complex activates caspase 8 which activates caspases 3 & 7.
4) Activation of executioner caspases provides +ve feedback to cell to produce more initiator caspases.
5) Caspase 8 provides +ve feedback to the mitochondria to release cytochrome C.
How are the cellular blebs cleaned up after apoptosis?
Phosphatidylserine is exposed on the outside of the cell which sends a signal to phosphatidylserine receptors on phagocytes to “eat” the cell that is exposing the phosphatidylserine.
How are the cellular debris cleaned up after necrosis?
Cells that undergo necrosis have DAMPs that become visible to the immune system after the cell has undergone necrosis.
Innate immune system recognises the DAMPs and macrophages become activated. They phagocytose cellular debris & DAMPs + release cytokines that initiate immune response.
Give examples of when apoptosis is used.
At the end of a cell’s life
During limb patterning in embryonic development.
Give examples of when necrosis happens.
When a cell has been damaged due to a pathogen, radiation or chemicals.
