Mutations in gerontogenes extend the number of divisions in cells. In necrosis, loss of ion gradients across the cell membrane leads to an influx of calcium and other ions, which triggers proteolysis and rupture of organelle membranes. Necrosis is a purely entropic phenomenon due to loss of the cell's ability to transform external energy. A defining feature of apoptosis is the fragmentation of the cell's DNA, produced by a regulated activation of deoxyribonuclease. However, several other biochemical processes that also lead to cell death are simultaneously induced.
Apoptosis is essential for normal development and remodeling.
Apoptosis has been implicated in several age-related diseases, including Alzheimer's disease. Theories of Aging There are more theories of aging than facts. Aging clearly occurs at different rates for different species, and even within a species, aging occurs at different rates among different individuals. The only reasonable conclusion is that aging must be genetically controlled, at least to some extent. Both within and between species, lifestyle and exposures may alter the aging process.