What Cells Must Die?
Apoptosis is used for many purposes. During the development of embryos, organs are shaped by building oversized structures and then pruning back the cells that aren’t needed. For instance, during development of the nervous system, half of the neurons die, leaving the proper neural wiring. If you have watched a tadpole lose its tail, you have also seen apoptosis in action. When you are an adult, apoptosis continues its work as obsolete cells die and are replaced by new cells, particularly in organs with high turnover such as the bone marrow and intestines. Apoptosis protects us from cells damaged by radiation or infected by viruses–when detected, these rogue cells are told promptly to commit suicide. Apoptosis is also one of our major defenses against cancer, and deadly cancer cells often have mutations that disable their own apoptosis machinery.
