Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!swrinde!mips!dimacs.rutgers.edu!aramis.rutgers.edu!athos.rutgers.edu!nanotech From: landman@eng.sun.com (Howard A. Landman) Newsgroups: sci.nanotech Subject: Re: Diamonds? Keywords: diamonds, bones Message-ID: Date: 10 Apr 91 02:03:32 GMT Sender: nanotech@athos.rutgers.edu Organization: Sun Microsystems, Mt. View, Ca. Lines: 43 Approved: nanotech@aramis.rutgers.edu In article toms@fcs260c2.ncifcrf.gov (Tom Schneider) writes: >So why don't living things use diamond? > >Cells handle carbon structures all the time, so why are shells and structural >components mostly silicon and calcuim? There are lots of possible answers. I think the most likely are: 1. It is difficult to build diamond at room temperature and pressure, and/or in aqueous solution. Life just never happened to randomly develop a mutation capable of doing that in a way that had survival value. 2. Carbon is already very valuable to living organisms, but silicon (and maybe even calcium) are not so valuable, nor so flexible in their uses. It makes sense to save the carbon for nanotech purposes (protein, DNA, energy storage) and use the simpler materials for bulk structural purposes. 3. Calcium comes in single-atom units that are easy to deposit. We don't really know how to grow a diamond one atom at a time, nor is there a plentiful source of single carbon atoms in most biological systems. (Energy metabolism is based on pairs of carbon atoms - crudely, burning acetate units.) Perhaps the best source is methionine, but such "active methyl" groups tend to be used for very specialized purposes. (There was a good overview article on folate/B12/methionine metabolism in one volume of Advances in Nutritional Research a while back.) Even then, you have a CH3- unit, so you have to figure out where to dispose of the hydrogens. In summary, there isn't a convenient source of "pure carbon" unbonded to other elements. Remember that "best" in a biological context is a very complicated notion. It involves questions of availability, feasibility, cost, simplicity and reusability (why do you have fingers on your feet?), as well as engineering considerations like strength. Further, you usually have to consider not just the organism but its competitors, food sources, predators and environment. -- Howard A. Landman landman@eng.sun.com -or- sun!landman