newbie question about DNA and cells

Bob xyzbbruner at uclink4.berkeley.edu
Sat Jan 3 14:08:17 EST 2004


On 31 Dec 2003 23:34:23 -0800, eric at pegasi.net (Eric Hanson) wrote:

>I'm coming to this from an information systems perspective.  The human
>body is arguably the most complicated information system on the
>planet.
>
>There is a problem in computer scientist called the Traveling Salesman
>Problem (TSP) that is one of the greatest unsolved problems in
>mathematics/comp. sci.  I'm exploring a theory that the human body
>seems to solve this problem.
>
>The traveling salesman problem states that a traveling salesman wants
>to visit for example the 50 capital cities of the US starting and
>ending in Salem, and travel the shortest route between them all. 
>Where does it go first from Salem?  Where after that?  Finding the
>optimal solution by trying all possible combinations is a simple
>algorighm but the number of solutions increases exponentially and
>after just a few cities it becomes computationally unfeasible to use
>this method.  People trying to "solve" the traveling salesman problem
>are looking for an algorithm that finds the optimal solution much
>faster than the brute force method, namely in polynomial time.
>
>To rephrase, the TSP deals with a problem where there are many nodes
>(cells) in a graph (body) and in order for a single node to know who
>its neighbors are as indicated by the shortest route through all
>paths, it has to have a bird's eye view of the entire graph and know
>the shortest route through it.  This seems to parallel what the human
>body does because for a single cell to know what piece of a liver it
>should be it needs to know its place in the entire liver and the
>entire body for that matter, or at least that's the theory I'm
>exploring.
>
>So a cell divides and the new cell starts expressing different genes,
>but maybe someone can answer me this.  _Where_ does it get the
>information to know which genes to express?  Is it from the cell it
>divided from, or from the extracellular cues or ...?  If the answer is
>too complicated or if it's just not known yet, is there a term for
>this area of study or you could point me more specifically towards
>something?

All of the above happen, in one case or another. The underlying issue
is asymmetry. Where does the asymmetry come from? It can come from
within or from without. Studies of development of the egg of
Drosophila (fruit-fly) is probably one of the best studied systems.

A couple of key points in comparing the cellular system to the TSP...
Remember, the cellular system arose by evolution. Thus "it works" is
the criterion, not "it is simplest". Further, because there are
various answers, knowing the answer in one case does not let you
predict what happens in another. OTOH, knowing many answers helps you
understand the range of answers that nature has discovered.

bob




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