Cancer and Apoptosis
Apoptosis is a type of programmed cell death. With respect to cell necrosis,
apoptosis is actively performed by cells. Apoptosis is generally induced by
physiological or pathological factors, which in turn trigger a series of cellular changes.
These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin
condensation, chromosomal DNA fragmentation, and global mRNA decay. And they
lead to characteristic cell changes (morphology) and death. For common
multicellular organisms, apoptosis is a normal physiological phenomenon. For
example, the average adult human loses between 50 and 70 billion cells each day
due to apoptosis; and human child between the ages of 8 and 14, approximately 20
to 30 billion cells die a day. Owing to apoptosis as a physiological process of a
determinant of cell fate, its balance is of great importance to the body. For instance,
excessive apoptosis causes atrophy, whereas an insufficient amount results in
uncontrolled cell proliferation, such as cancer. Therefore, apoptosis is rigorously
regulated by suppressor and pro-apoptotic factors.
In contrast to necrosis, which is a type of traumatic cell death that results from acute
cellular injury, apoptosis is a highly regulated and controlled process that confers
advantages during an organism ’s life cycle. Specifically, apoptosis is generally
brought about by physiological or pathological factors, the necrosis is mainly caused
by lack of oxygen, and the two can be readily distinguished by observation. In the
process of apoptosis, the cells shrink and the DNA is degraded into 180bp-200bp
fragments by endonucleases. Unlike necrosis, apoptosis produces cell fragments
called apoptotic bodies that phagocytic cells are able to engulf and remove before
the contents of the cell can spill out onto the surrounding cells and cause damage to
them. When the cells are necrotic, the cells swell, the cell membrane is destroyed,
and the permeability changes. The organelles are scattered into the intercellular
substance and require removal of macrophages, resulting in inflammation of the
local tissue. According to previous studies, apoptosis is a more common form of cell
death than cell necrosis. For example, separation fingers and toes in a developing
human embryo occur because cells between the digits undergo apoptosis.
