ageing rates in different species

Jud Cooley cooley at fps.com
Mon Aug 5 13:13:26 EST 1991

       The recent issue of Scientific American (August, 1991), which has a good
   article on "Telomeres".  Telomeres are the DNA sequences at the end of the double
   helix.  In humans, this sequence is TTAGGG repeated some large number of times.  It
   is on the end of ALL human chromosomes, and on the end of the chromosomes of ALL
   species studied (appr 100 vertebrate species that have not had a common ancestor
   for over 400 million years).

        It has also been noted that cellular DNA replication often "truncates" the DNA
   molecule.  My reference is the article itself, and a report in "Foresight Update No. 10",
   from the Foresight Institute, which briefly profiles the work of Harley, et al. at
   McMaster University and Cold Spring Harbor Laboratory (Nature 345:458-460, 31May90)
   Organisms that do not age have "telomerase" enzymes that "repair" the truncation.
   Higher organisms have these enzymes as well, but they are only active in the production
   of reproductive cells. 
        The Foresight Institute article gives an approximation of 180 cell divisions
   in human somatic cells before the telomeres are exhausted.  The speculation, of course,
   is that this may be the cause of cellular death due to ageing.

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