Are you aware that, day in and day out, your body may be replacing cells at the rate of about 1 million cells per second? Sometimes cells have to die so that other cells (and the rest of the body) may live – a concept first studied in tadpole tail shortening as early as 1842. But it wasn’t until 1990 that science had the tools to explore programmed cell death systems in detail. Some of those studies resulted in Sydney Brenner, Robert Horvitz, and john Sulston receiving a 2002. Nobel Prize in Medicine for what we now call apoptosis or programmed cell death. Ongoing research continues to demonstrate the importance of apoptosis in understanding various types of cancer, autoimmune diseases, and normal growth and development. That apoptosis does not refer to cells that die because of some type of injury I emphasize by the title to this reading. What is going on here is a natural, multiple, sequential step (programmed) process in which a cell kills itself or commits suicide. When embryos develop normally, some early cells have to be removed, akin to taking down the scaffolding and concrete forms after we have completed parts of a building. Normal genes in these cells turn on and start the program that leads to their removal. Some non developmental cells may be affected by external stimuli that trigger apoptolis that leads to their demise. Examples here would be cells infected by a virus, cells that incur DNA damage, or cells that have turned cancerous. Each of these scenarios would normally start apoptosis in the affected cells, thus removing them from the cell population.
A number of highly complex mechanisms may initiate apoptosis, but once that happens, the sequential steps begin with the cell shrinking, its surface bubbling outward, and its DNA and some cell proteins digested and recycled. The mitochondria within break down ad release cytochrome c as the cell collapse into tiny vesicles releasing both ATP and UTP, which signal passing phagocytic cells (cells that consume microorganisms and debris of dead cells) to gather around and eat. The complexity of mechanisms, receptors, and choreography of events for accomplishing apoptolis is stunning and appears to be a carefully designed system to protect cells from disease and enable them to undergo normal growth and development.