Why and when does apoptosis happen?

Question

Why and when does apoptosis happen?

Answer 1

Apoptosis is also called "Programmed Cell Death" and it is the process by which a cell will kill itself through internal proteases and nucleases.

It can be triggered by a number of internal or external signals.

For example, if the DNA of a cell is damaged to a degree where the cell is unable to repair itself - mechanisms will signal the cell to kill itself, in order to prevent cancerous transformation.

Cells can also be induced to apoptose by external signals. For example, if a neuron during development fails to form the correct connections to other cells, it will initiate apoptosis (90% of all neurons formed during development do this). Alternatively, if a cell finds itself on the "wrong" sort of extracellular matrix proteins (meaning it is in the wrong location in the body), it will apoptose (this is called "anoikis"). Signalling proteins can also tell a cell to kill itself: if an immune cell encounters a virus-infected cell, it will tell the infected cell to commit suicide.

Apoptosis can also occur inappropriately. For example, Huntington's disease is caused when a subset of neurons undergo apoptosis when they should not.

Answer 2

Apoptosis is a type of cell death in which the cell uses specialized cellular machinery to kill itself; a cell suicide mechanism that enables metazoans to control cell number and eliminate cells that threaten the animal's survival.