Apoptosis Flashcards
What is apoptosis?
Cell death with shrinkage - an active process
When does apoptosis occur?
Sculpting
Killing virus infected cells
DNA damage
Graft vs host disease
What does apoptosis look like?
Condensation
Fragmentation - buds
Apoptotic bodies
How does apoptosis occur?
Three phases
- initiation
- execution
- degradation + phagocytosis
How does initiation and execution occur?
Triggered by intrinsic and extrinsic mechanisms
Result in activation of caspases
What are caspases?
Enzymes that control and mediate apoptosis
Cause cleavage of DNA and proteins of the cytoskeleton
What is the intrinsic pathway?
Initiating signal comes from within the cell
What are the triggers of the intrinsic pathway?
DNA damage
Withdrawal of growth factors or hormones
What is the mechanism of the intrinsic pathway?
p53 is activated
Outer mitochrondrial membrane becomes leaky
Cytochrome C is released
Activation of caspase 9
What is the extrinsic pathway?
Initiated by extracellular signals
What are the triggers of the extrinsic pathway?
Dangerous cells
- tumour cells
- virus infected cells
What is the mechanism of the extrinsic pathway?
TNFα secreted by T killer cells
Binds to cell membrane receptor
Activates caspase 8
Caspase 8 activates caspase 3
What happens to apoptotic bodies?
Phagocytosed
