The purpose of this paper is to examine how the human cell survives. The paper examines two specific sets of factors associated with survival, the processes and mechanisms that lead to continued cell life and the processes and mechanisms that lead to cell death. This two-fold examination is made because it is only by examining both processes that a complete understanding of cell survival be attained.
All living organisms consist of cells, which divide and multiply. As noted by Campbell and Reece (2001), with the exception of bacteria and blue-green algae, all organisms are composed of eukaryotic cells, which have their genetic information in the chromosomes which is located in a nucleus separated from the rest of the cell, the cytoplasm. The cells live by increasing in size and making exact replicas of all of their genetic material.
The process of cell division (cell proliferation) is characterized by four distinct phases which have been discussed by Alberts, Johnson, Lewis, Raff, Roberts, and Walter (2002). The GI phase, according to Alberts et. al (2002), is the first phase of the cell cycle in which cells grow in size and are receptive to signals that are external to the cell itself. Such signals include soluble growth factors and intracellular contact. At some point, these signals can operate to trigger the cell to begin the second phase of the cycle.
During the G1 Phase, the cellÆs metabolic rate is high and many proteins are made. As these proteins are phosphorylated by a process known as protein kinases, the cell moves toward the end phase of the cycle known as ôthe restriction point.ö Campbell and Reece (2001) point out that prior to the restriction point, a cell will stop growing if soluble growth factors are not present. However, once the restriction point is reached, the cells will continue to progress through the remainder of their life cycle regardless of whether these factors are present.
It is activa...