The human telomere, a simple repeating sequence of six bases, TTAGGG located at the ends of chromosomes (Moyzis et al, 1988) protect them from degeneration, reconstruction, fusion, and loss. It is believed that this shortening becomes critical for a telomere on a particular chromosome, which becomes unstable and the cell stops dividing.
Nevertheless, as human dermal fibroblasts of 100-years-old individuals still have a telomere length of 6–7 kb and retain proliferative capacity for about 20 doublings (Allsopp et al, 1992). They have not reached the limit of their proliferative capacity or of telomere shortening even at such an advanced age. The telomere length of human peripheral blood lymphocytes decreases with age and shortens to about 5 kb in some individuals after age 60 years, but no individuals have been found with a mean telomere length of less than 5 kb, even among 100-years-olds. (Vaziri et al, 1993) (Iwama et al,1998)
Does this Telomere length shortening actually cause our cells to age and malfunction?