<br><div><span class="gmail_quote">On 1/26/06, <b class="gmail_sendername">Brett Paatsch</b> <<a href="mailto:email@example.com">firstname.lastname@example.org</a>> wrote:<br><br></span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div><font face="Arial" size="2">The unit of biology is the cell not the atom. Its
the cell that does the replicating and any particular human body we
have experience of to date has developed from cells, not atoms.</font></div></blockquote><div><br>Let me state this very clearly -- self-replication is *NOT* necessary for "real nanotechnology" (at least in my book). Josh Hall wrote a paper 5+ years ago demonstrating quite clearly that nanotechnology assembly lines could be very fast. Put another way a specific dedicated assembly process can be much more efficient than a general purpose assembly process. This relates to the "broadcast" architecture for nanorobotic assembly methods -- you do not have to replicate the subcomponents which store and retreive the information (DNA & RNA in cells). All that is required is the receiver for the instruction scheme. This corresponds someplace between SIMD and MIMD in computer architectures -- but not general purpose self-replicating assemblers.
<br><br>While some people view self-replication as a goal to be achieved (i.e. 'we have created life') I tend to view it as misdirected energy which could be better utilized designing nanoscale parts and/or nanofactories for them. We already have self-replicating, relatively general purpose assembly systems (bacteria) which we have been and continue to engineer for various purposes.
<br></div><br>The advantage a "cell" has over "soup" is that it allows for reactant concentration and speeds up the rates at which molecules can be broken down and/or reassembled. That becomes largely irrelevant when nanofactories are fed relatively pure small molecule reactant streams. (Why do you think I wrote the paper about the assembly of an aircraft carrier from an oil pipeline???).
<br><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div> DNA does not
replicate on its own. Ribosomes don't work outside of their cellular
environments.</div></blockquote><div><br>DNA is replicated using a reactant pool (esp. Primers, DNA bases & ATP) and a single molecular machine (one of the various DNA polymerases). This is the entire basis of PCR amplification (replication) of DNA. DNA replication does not require a cell. DNA polymerases are molecular machines that I would guess are around 10-20nm in size (still smaller than current scale lithography). Extracellular production of proteins from RNA is also feasible (I believe you can buy kits for this from the molecuar biology companies). Whether all of the components on the kits are produced de novo or whether some are isolated from cells I do not know. But the chemistry and biochemistry for the production of all of the necessary molecular machines for these processes is well known. It is simply a cost issue of whether it is cheaper to do the reactant synthesis from cheap materials or separate the already built reactants from biological systems.
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<div><font face="Arial" size="2">The *generally* in that sentence is one hell of a
hard working word. </font></div></blockquote><div><br>Actually, it is "biological systems" that may be the point of confusion. I was *not* refering to self-replicating biological systems which probably require a minimal size of 200-300nm, more probably 500+nm (I'll believe nanobacteria exist when I see the genome sequence for one deposited in a database). What I was refering to was biological disassembly or assembly systems (everything from single enzymes to enzyme complexes to enzyme systems). Those I believe fall into the 5-20nm range. There may be a few that are somewhat larger but I doubt many are larger than 100nm (though obviously the protein chain could be longer).
<br></div><div><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div><font face="Arial" size="2">But there are feedback mechanisms in place such
that glycolysis operates sometimes and gluconeogenesis other times and various
GLUT receptors on various types of cells are sensing different levels of blood
glucose. [snip]</font></div></blockquote><div><br>Yes of course. I was talking about systems that would circulate *only* small molecules such as glucose. Both the kidney and dialysis machines are examples of systems which allow selective transport of various molecules from one side of a membranes to another (look up their wikipedia entries or see ). In fact you could get the same effect by inhibiting the transporters in the kidney which reabsorb glucose. The reason that diabetics have sweet urine is that the blood sugar glucose levels are so high that they overwhelm the reuptake transporters .
<br><br>But rather than taking a drug to inhibit glucose reuptake it seemed much cooler to plug yourself into something which uses the glucose for a useful purpose. Damien is right about the connection problems of course. But this is something that people are working on very intensely because they want to monitor blood glucose levels and be able to have a computer administer insulin as required. There are different routes being pursued towards this which involve implanted and external solutions which obviously have different advantages and disadvantages.
<br><br>Robert<br><br>1. <a href="http://arbl.cvmbs.colostate.edu/hbooks/molecules/hexose_xport.html">http://arbl.cvmbs.colostate.edu/hbooks/molecules/hexose_xport.html</a><br></div></div><br>2. <a href="http://science.uwaterloo.ca/~mpalmer/MetabolismNotes/page-14.7.html">