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Hi, folks -
I just got in Behe's book, and will read it as soon as I can (but my
parents arrive for a week visit tomorrow, so it won't be in two days ; -
)). Before reading it though, I thought I would share one example that Behe
may or may not discuss.
There is an extremely important metabolic pathway called the citric acid
cycle which in us and in almost all organisms is used to burn fuels (both
fats and sugars) and to make new building blocks of several kinds. The
pathway is a cycle: there are enzymes that pass the changed molecules on to
the next one and the path comes back to itself to repeat. The path is
useful because you can feed in four-carbon molecules and get out two
two-carbon molecules and some energy (among other ways to use it).
Now, blue green algae (which are very ancient - fossils dating back 3.5
billion years) don't have this cycle, and they can't grow on sugar for that
reason; they have to make all their own fuel and they don't grow in the
dark. How come? Where did the citric acid cycle come from? Well, it turns
out that the blue green algae do have all of the enzymes of the cycle,
except for one. What use is this "incomplete" cycle? It turns out that if
you look at the "broken" cycle with that question in mind, you notice
something very interesting: each half of the cycle is useful for something
in its own right. The "right" half of the cycle is good for making amino
acids and the "left" half of the cycle makes compounds that are needed for
making chlorophyll and other energy related molecules. So, even without the
enzyme that closes the cycle, all the other enzymes are useful.
Then how did the cycle come about? It turns out that the enzyme that closes
the cycle is very similar to the enzyme that feeds fuels into the pathway.
It would only have taken a few amino acid changes to change one into the
other, so the parsimonious guess is that some organism had a mutation like
that, and now it could grow in the dark or by using other fuels. Since that
would be very useful, it is easy to see how it spread.
My point is this: sometimes the evolutionary roots of things aren't visible
unless you know a lot of organisms and look to see uses that aren't the
ones that are taught in the textbooks. Especially in metabolism there is a
great deal known that just plain doesn't fit into the texts. When I read
Behe I will be looking to see how far back he looks for these kinds of
connections and if he doesn't I have people here that I can ask. It looks
interesting, though.
Peace and joy +
Alice
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alice-fulton@uiowa.edu
http://solon.cma.univie.ac.at/~neum/sciandf/fellow/welcome.html