When Dr. Leonard Hayflick performed his experiments using human cells grown in a culture, he managed to pull back the curtain on an ancient process that essentially prevents immortality. The process of cellular death exists within our genetic code. The nucleus of a diploid cell (a cell with two sets of chromosomes) is comprised of DNA information contributed by each of an organism's parents. Since the key to the Hayflick limit is found in the cell's nucleus, we are basically programmed to die. Why is this?
There are several reasons why a cell should be programmed to die after a certain point. In the developmental stages, for example, human fetuses have tissue that creates some webbing between our fingers. As we gestate, this tissue undergoes apoptosis that ultimately allows our fingers to form. Menstruation -- the monthly process of shedding the lining of the uterus -- is also carried out through apoptosis. Programmed cellular death also combats cancer (defined as uncontrolled cellular growth); a cell that turns cancerous still has a life span like any other cell and will die out eventually. The drugs used in chemotherapy are meant to accelerate this process by triggering apoptosis in cancerous cells.
Apoptosis is the result of several signals from both inside and outside a cell. When a cell stops receiving the hormones and proteins it needs to function or sustains enough damage to stop functioning properly, the process of apoptosis is triggered. The nucleus explodes and releases chemicals that act as signals. These chemicals attract phospholipids that engulf the cell fragments, degrade the individual chromosomes and carry them out of the body as waste.
Clearly, apoptosis is an intensely regulated and highly refined process. How, then, could we ever possibly thwart it? Let's find out on the next page.