RE: Metal transport (was: platoon stuff and combat engineers)

G'day,

> Beth, perhaps you can shed some light on this. Seems an 
> appropo time to bring it up.

My biochem is shaky I'm much more an ecological theorist, but I'll have
a
crack (then maybe John Lambshead or someone can correct me).
 
> I don't know of any structural uses of metal or metallic 
> compounds. Why not? Just because the useful metals are 
> not as chemical active as Ca? (and the ones that are 
> active aren't common) Fe seems to have plenty of useful
> reactivity, considering we use it to transport O2 ourselves.
> 
> Are there are chemistry- or physics-related reasons why metal 
> structures aren't found in nature? (real answers, theories, sheer 
> guesses and tall stories all welcome)

Based on my limited biochem knowledge (I dodged uni chem by doing math)
its
due to the chemical properties of metals. Metals have to be in specific
forms to be biologically available in the first place (e.g.
methylmercury vs
pure mercury) and then its a matter of how much it takes to gum up the
biological works by overloading receptor sites etc. For instance some
metals
can overwhelm/change receptors that are there for another purpose (in
much
the same way as carbon monoxide will block haemoglobin from carrying
oxygen). Biological structures can often cope with some metals, but too
much
is a bad thing. That's why we need a certain amount of iron to keep the
body
up to its full potential, but too much and you've got severe blood
chemistry
imbalance and the potential for damage to major organs. Its particularly
a
problem in multicellular organisms so bacteria can more readily handle
metals or concentrations other organisms would find toxic. So for Terran
animals I'd say for those metals that are not currently utilised already
(so
calcium is, but to my knowledge nothing uses gold (say) as a major
intentional skeletal component) that in trying to get enough material
together to make a support structure they'd end up poisoning themselves
or
if they had to purify it so it couldn't flood back into their system
then
many metals may end up being to brittle compared to the strength of
things
like chitin.

Sorry I can't be more precise