Programmed cell death (apoptosis)
In its DNA or "instruction manual/instruction bool", each cell has a "suicide program" which is triggered by certain signals. This programmed cell death, called apoptosis in the terminology of molecular biology, is an important process.
Here are some examples of apoptosis:
During the development of an organism, for instance, some cells need to be removed again. The human embryo at first develops "webs" between the fingers and toes. Later these must be removed again. To do that, the "suicide program" in the skin cells of the fingers becomes activated, causing the "web" to degenerate.
Moreover, old or dysfunctional cells are removed through apoptosis. Programmed cell death also is an important backup system that guards against unrestrained cell proliferation or eliminates highly damaged cells. It is initiated in response to mutations in a cell's genetic material or other signs of an abnormality. Cancer cells do not respond to signals triggering the apoptosis program; in fact, an important step in becoming a cancer cell is gaining the ability to evade the programmed cell death.
The death message is often transmitted by messenger substances from outside the cell, which dock onto certain proteins on the surface of the cells. These docking sites are therefore called "death receptors". They function like tiny antennas. Due to the docking the antenna becomes deformed. That is a signal for the cell to activate special miniscule "scissors" which ultimately kill the cell. These scissors cut up certain proteins that are important for the survival of the cell, thus bringing about the cell’s death.
"Programmed cell death" can be triggered by another process, through substances in the cell itself that are bound to the cell scaffolding. When the cell is damaged beyond repair - e.g. by ultraviolet light – these messenger substances are released by the cell scaffolding and trigger apoptosis.
