Is there a "life clock" in the human body? Here, the "life clock" refers to a "timer" that records everyone's lifespan and an "indicator" that shows life's inexorable march toward its end. Does it really exist? Where is it? This question has long puzzled people. After years of research by scientists, the "life clock" has finally been found. Its official name is "telomeres".
"Telomeres" are the ends of chromosomes. Each chromosome has two ends, so there are two "telomeres". Some people compare chromosomes to shoelaces, with telomeres being the tips of shoelaces. Although the tips of shoelaces share the same components as the rest of the shoelace, they are more robust, indicating that the structure of the tips differs from the rest of the shoelace in some ways. This is indeed the case. The most important component of chromosomes is DNA, which is composed of deoxyribonucleotides carrying the four bases A, T, G, and C, paired according to the A-T and G-C rules. In addition to the double helix structure, telomeres also have a single-stranded structure. The telomere DNA is mainly composed of repeating units of TTAGGG, with 500 to 5,000 such repeating units.
Scientists have found that during cell division in the human body, the telomeres always shorten, or that some base pairs are lost from the telomere DNA each time a cell divides. Chinese scholars such as Tong Tanjun found that when human fibroblasts are cultured in the laboratory, the telomeres shorten by about 49 base pairs each time they divide. If we calculate according to the division limit determined by Hefler, human cells divide 50 times. Each division results in the loss of 49 base pairs. When the telomeres lose 49×50 = 2,450 base pairs, the fibroblasts will no longer proliferate. Cells that cannot proliferate mean aging and death. Therefore, the "life clock" in fibroblasts has 50 "notches", each separated by 49 base pairs. When the telomeres lose 2,450 base pairs, the "life clock" becomes the "doomsday bell" that is about to ring.
Since normal human activities require cell division and proliferation, once all the proliferating cells in the human body sound the doomsday bell, human lifespan will naturally reach its limit, and people will truly reach the end of their days.