L8: Cell death

Summarise the main differences between apoptosis and necrosis

Apoptosis- programmed cell death, a defence mechanism. Broken down in a controlled homeostatic process. Occurs to make space for younger cells.

Necrosis- Undesirable and usually from cell injury, cells swell and burst releasing cell content (inflammation)

Give an example of apoptosis

Regression of tadpole tail to frogs

What is the definition of apoptosis?

To destroy cells that represent a threat to the integrity of the organism

How does apoptosis occur?

Cell is broken down from within by caspases (proteins)

Caspases need to be activated- extrinsic or intrinsic

Outline the role of caspases in triggering apoptosis

Caspases are called cell death proteases

Synthesised as in-active pro-caspases. Initiator caspases activate a cascade generating lots of effector (executioner) caspases

*—→ **—→ ***

Describe the extrinsic pathway

Initial signal comes from outside of the cell

• Receptor spans outside membrane

• Adaptors

• Disc formation

• Caspase 3 activation (execution pathway). Point of no return. Complicated steps to prevent accidental cell death

Describe the intrinsic pathway

Mitochondrial change

MPT pore

Caspase 9 activation

Caspase 3 activation (execution pathway)

What is autophagy?

A self eating process, degrading the cytoplasmic constituents and organelles in the lysosome

What is the role of autophagy?

Self defence mechanism activated by cell during starvation

How is autophagy different from apoptosis?

Expression of specific markers