Cancer and Apoptosis

1. 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.