feedback requested on ideas(modified)

Aubrey de Grey ag24 at
Fri Feb 23 12:39:20 EST 2001

Iuval Clejan wrote:

> Damage to proteins or RNA is irrelevant, because they are just degraded
> and replaced. Their lifetime is pretty short compared to the lifetime
> of an organism.  DNA lasts as long as the organism.

This is an oversimplification.

First, Julian's example of prions is not as much of a special case as
it may sound: the junk in lysosomes is partly proteinaceous and partly
lipid, the proportions varying between different cell types, yet it's
indefinitely long-lived and certainly harmful.  Similarly outside cells,
the plaques that accumulate in Alzheimer's brains (and also to a lesser
extent in everyone's brains), as well as non-brain amyloid, are also
indefinitely long-lived and quite probably bad for us.

Second, damaged DNA only lasts as long as the organism if it is in cells
that don't divide, or in cells in which the damage doesn't promote the
death and replacement of the cell.

On the other hand, some proteins that are often said to be indefinitely
long-lived are in fact turned over -- slowly, but not as a proportion of
organismal lifespan: collagen is a prime example.

I think that things like the above should definitely be included among
the ever-failing inter-dependent structures that Julian described.  To
call them "information structures" may be a little risky insofar as it
recalls Orgel's error catastrophe theory, which is no longer in favour,
but that's a pedantic point.

Aubrey de Grey

More information about the Ageing mailing list