Apoptosis: programmed cell death

In short: Apoptosis is an orderly self-destruction programme that lets cells die in a controlled way when they are no longer needed or have been damaged. It is essential for the development and health of multicellular organisms.

In more detail: Unlike uncontrolled cell death, the cell does not burst during apoptosis but breaks itself down into small packages wrapped in membrane. These are taken up by scavenger cells without causing inflammation.

In detail

• Process: The cell shrinks, its genetic material condenses and is cut into pieces, and the cell membrane forms bulges from which so-called apoptotic bodies arise.
• Difference from necrosis: In necrosis, for example after injury or lack of oxygen, the cell swells and bursts; its contents spill into the surrounding tissue and trigger inflammation.
• Caspases: The actual dismantling is carried out by caspases, a family of protein-cutting enzymes that activate one another in a chain.
• Intrinsic pathway: When a cell is badly damaged, for example in its DNA, the mitochondria release the protein cytochrome c, which sets the caspase cascade in motion.
• Extrinsic pathway: Other cells, especially immune cells, can give the signal for apoptosis from outside via so-called death receptors on the cell surface.
• Body development: In the embryo, fingers form because the skin cells between them disappear through apoptosis; surplus cells in the nervous system are removed in the same way.
• Immune system: Immune cells that would attack the body itself are weeded out by apoptosis, and virus-infected cells are driven to cell death by killer cells.
• Relevance to cancer: Cancer cells often escape apoptosis, for example when the protective protein p53 is altered; many cancer treatments aim to trigger cell death in tumour cells again (zelle-aufbau-und-funktion, lysosomen-und-zellverdauung).