Re: scientific american

Date: Mon May 29 2000 - 10:24:34 MDT

Daniel writes:
> I think _American Scientist_ is much better in regards to nanotechnology and
> life extension -- more interested in examining the ideas rather than
> dismissing them. The current issue has the nanotechnology article
> "Biomolecules and Nanotechnology." A previous issue had an examination of
> slowing down aging and some of the problems involved in life extension from
> an engineering perspective. The former is now online at:

This was an interesting and easy-to-read article which provided an
insightful view on some of the organizing principles used by life in
constructing its version of nanotech.

Cells are constrained by the materials they have to work with, and by
the fact that the error rate in constructing proteins prevents them
from building ones beyond a certain size. So what they do is build
them with self-assembling sub-units. If a sub-unit is malformed due to
an error, it won't fit with the others and so it won't be picked up in
the self-assembly. At least that seems to be the theory.

The interesting thing is that many large protein complexes are built out
of repeated copies of a single protein, which self-assembles with itself
to produce a linear or ring structure. Sometimes a few more proteins
are used as components, but when this happens the repeated units are
arranged symmetrically. Perhaps this is advantageous because you get
the effect of a large structure by coding for just a single protein.

I wonder what happens to proteins which get built with errors? They won't
self-assemble and will just float around, useless. There must be some
other machinery which takes them apart, but it would seem hard to take
apart an arbitrarily error-loaded protein. Maybe everything in the cell
gets periodically swept into a lysosome and dissolved?

Cells also have to work with the fact that their machinery is somewhat
soft and floppy. They exploit this rather than work around it,
making machines that wouldn't work if rigid. The article describes
this by saying that cellular machines "breathe", that is, they flex,
expand, contract, open and close slightly all the time. Many machines
wouldn't work at all without breathing; in some cases the active sites
are buried inside the complex and are inaccessible until a crack or
crevice breathes open.

All this provided a fascinating picture of how different the engineering
principles used by cells are from how humans design things. However these
ideas didn't sound like they would be applicable to current plans for
nanotech. Hard nanotech won't have the same constraints, limitations,
and, yes, flexibility of biotech components.

It is unlikely that nanotech designs would breathe in the biological
sense; if this function were needed there could be something like a
mechanical bellows hooked to clockwork latches which would open and close.

Also, the limitations on error-free assembly of large complexes won't
apply to nanotech, so there will be no need to rely on building smaller
components that self-assemble, and therefore probably no particular
reason to use symmetry to the same extent as is done in biology.


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