> apoptosis ...limiting ... the age (in # of cell divisions) that a particular
> cell can have (and thus effectively limit exposure to damage or mutation from
> radiation). This seems to require genetic markers on the DNA strand that
> essentially count the number of times a cell has divided. If so, during
> Mitosis would this distinguish the new cell from the one it just divided from
> (so they are not 'identical')?
If there is some kind of genetic marker (or counter) that gets incremented
(and passed down to the daughter cells) every time there is cell division, then
all cells drived from a single cell would die at about the same time. Therefor,
as has been stated, this counter must be partly under environmental control
and modulated by the differential process.
The whole idea of AGE is very interesting in autopoietic systems. If a parent
cell divides (and results in two daughter cells) which daughter cell is older?
The environment seen by each daughter cell (symmetry breaking) must influence
their differentiation and thus their apparent age. And what exactly is aging?
Is it just the time since last division? Is it some efficiency in the
self-producing process? As Don recently pointed out, Rosen has suggested that
complex systems have internal models of some aspect of their own operation (self
reference) that are used in their operation....these internal models will
eventually fail to be effective predictors...and the system will have more and
more difficulty counteracting degredation by the environment. Perhaps
mitosis, in a way, re-synchronises "the model" back up....
Onar writes:
> Death follows in the wake of birth, leaves fall of in the fall and new ones
> grow out in the spring, species go extinct and new ones
> pop into existence. All this suggests that the conditions for larger scale
> organizational closure are satisfied. In this sense life on earth is not
> "untamed", there is a natural self-taming in the cancellation of all kinds of
> growth. Therefore, while death may be an evolutionary accumulated imprecision
> it is also a very common biological "plan" and has important biological
> functions on all scales of life.
lysosomes chew up old proteins
ribosomes manufacture new proteins
apoptosis results in a cell death
mitosis results in an additional cell
a multicellular organism dies
a multicellualr organism is born
a species becomes extinct
evolution results in an additional species
changeless change.
Jeff Prideaux