BIO211 Apoptosis Notes

How Cells Die

• Cells can die through:

  • Necrotic cell death: Usually due to trauma.

  • Apoptotic cell death: Programmed cell death.

    • Results in apoptotic bodies.

    • These bodies are ingested by other cells.

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Why Apoptosis Occurs

• Removal of unwanted cells during development.

  • Example: Removal of tissue between digits.

  • Example: Loss of tail in tadpoles.

• Pruning the number of neurons to regulate connectivity.

• Regulating the size of constantly regenerating tissue, such as the liver.

Apoptosis as a Balance

• Apoptosis is a balance between pro-apoptotic and anti-apoptotic signals.

• Survival factors promote cell survival and suppress apoptosis.

• Mitogens stimulate cell division and overcome cell cycle blocks.

• Growth factors stimulate cell growth and inhibit the degradation of macromolecules.

Intrinsic vs. Extrinsic Apoptosis

• Intrinsic Apoptosis:

  • The apoptotic signal originates from inside the cell.

  • Involves proteins such as BAX, BAK, BAD, BID, BIM, BCL-2 etc.

  • Some are “pro” apoptosis, some “anti”.

• Extrinsic Apoptosis:

  • The apoptotic signal originates from outside the cell (other signals).

• Both types lead to the activation of Caspases.

Caspase Activation

• Caspases are cleaved to form active molecules.

• Cleavage is irreversible.

• Two inactive procaspase molecules undergo cleavage and assembly to form one active caspase molecule.

Caspase Cascade

• Cleaved caspases initiate a