The Teleomere problem
Each
chromosome consists of a single, very
long dsDNA molecule.
(Left)
Removal of lagging strand RNA primers
(in red) leaves an unpaired region at
the very end of the molecule, which if left
single-stranded would be
degraded, also exposing the paired ssDNA region..
The enzyme Telomerase adds
extra DNA onto
the end of
both fragments, based on an RNA template (centre). These Telomere
sequences are
seen as fluorescently stained terminal bodies in the
photograph at right. Telomeric
DNA may be lost
during subsequent round of chromosome replication, without
loss of
critical chromosomal DNA.
Experiments
suggest that telomerase function is less efficient as
cells age,
and that the limited lifespan of cells in culture, and
perhaps aging of in
vivo cells as well, is a
function of the loss of critical DNA.
For their work on telomeres, Drs Elizabeth Blackburn, Carol Greider, and John Szostak were awarded the Nobel Prize in Physiology or Medicine for 2009.
For their work on telomeres, Drs Elizabeth Blackburn, Carol Greider, and John Szostak were awarded the Nobel Prize in Physiology or Medicine for 2009.