cels alive 6- cell death Flashcards
what are the 3 types of cell death?
Necrosis
Apoptosis
Autophagy
Describe necrosis
Non-programmed cell death
Non-physiological process (not regulated)
Sudden death
Describe apoptosis
Programmed cell death
Homeostatic mechanism
Can be defence mechanism
Describe autophagy
Survival mechanism
Can lead to cell death
Starts organelles digestion
When does necrosis occur?
After acute insult e.g. lack of blood or trauma
What happens during necrosis?
Cells swell and burst
Inflammation occurs because of the release of cell contents
what does apoptosis require?
ATP
Give 3 examples of apoptosis
Regression of tadpole tails
Removal of interdigital webs during limb development in frogs
Formation of synapses requires surplus cell removal
Describe the process of positive selection during apoptosis
Lymphocytes are selected on their ability to respond to MHC proteins and foreign antigens
May be stimulated to undergo apoptosis if they don’t respond optimally
Describe the process of positive selection during apoptosis
Lymphocytes are selected on their ability to respond to MHC proteins and foreign antigens
May be stimulated to undergo apoptosis if they don’t respond optimally
What types of cells can be targeted by apoptosis?
Cells infected with viruses
Cells with DNA damage
Cancer cells
Cytotoxic T lymphocytes (can induce apoptosis but are destroyed when no longer required)
Describe the caspase cascade in cell death
Caspases are cell death proteases
Synthesised as inactive pro-caspases
Activated by each other by cleavage
Small numbers of initiator caspase activate a cascade generating lots of effector (executioner) caspases
They cleave cellular components: nuclear lamina, activate DNAses and other structual proteins
Activation is complete and irreversible therefore tight regulation throughout is essential
What negative intracellular signals trigger the intrinsic pathway of apoptosis?
Absence of growth factors and hormones
Loss of factors which usually suppress activation of apoptosis
What are the positive intracellular signals that trigger the intrinsic pathway of apoptosis?
Radiation
Toxins
Hypoxia
Viral infections
Describe the process of the intrinsic pathway of apoptosis?
Changes in mitochondrial membrane
- changes in mitochondrial membrane
- Opening of MPT (mitochondrial permeability transition) pore
- Release of mitochondrial proteins into the cytoplasm e.g. cytochrome C
- Binding of cytochrome C to pro-caspase 9 leading to activation
Which members of the Bcl2 protein family are:
a. anti-apoptotic?
b. pro-apoptotic?
a. Bcl2 and Bcl-X
b. Bax, Bid and Bad
What is the extrinsic pathway of apoptosis ?
-Binding of death ligand to the receptor
- adapter proteins interact with death ligand through death domain
- a DISC: death including signaling complex is formed
- Receptors aggregate + cause cleavage/activation of caspase 8
activates cascade
features of an apoptotic cell
cell surface has budding (bleb appearance)
cell and nucleus shrink
chromatin condenses
cleavage of nuclear proteins and nuclear DNA
What is the intrinsic pathway/caspase cascade triggered by?
damage or stress
What is autophagy?
Cell self-eating process leading to cell death
Catabolic process that degrades cytoplasmic constituents and organelles in the lysosome
self defence mechanism activated by cell during starvation
How is autophagy different from apoptosis?
Expression of specific markers in autophagy (ULK, Beclin and LC3)
Autophagy can inhibit apoptosis
Autophagy is reversible
How is autophagy different from apoptosis?
Expression of specific markers in autophagy (ULK, Beclin and LC3)
Autophagy can inhibit apoptosis
Autophagy is reversible
What are caspases?
Cell death proteases.
Synthesised as an inactive ‘procaspase’.
Activated once cleaved because it loses its inhibitory region.
