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Re: Carboniferous Endothermy

TomHopp@aol.com has stuck his neck out with claims such as:

>     Regarding endothermy, it may seem like we'll never get the
> origins of this physiological process out of the fossil record, but
> don't you bet on it.  The hypothalamus regulates body temperature
> via nervous and hormonal signals to such body parts as brown fat
> tissue, skeletal muscle (for shivering) and a bunch of as-yet-poorly
> understood metabolic pathways.

Anybody interested in evaluating Tom's claim while studying molecular
biology might consider looking for genes related to the UCP genes.
>From what I know (and from a database search I just performed) these
genes are only known directly from primates and rodents.  It would be
interesting to find out if they exist in, for example, frogs and
chickens, and even more interesting to see if their functions there
are at all similar to their functions in mammals.  UCP stands for
"uncoupling protein", and the things that the UCP's uncouple from each
other are metabolic activity and the creation of energy-storing
molecules.  Much of the energetics in eukaryotes is driven by the
production of ATP in the mitochondria.  The mitochondria create a
proton gradient across their inner membrane by coupling glycolysis
(i.e. the buring of sugars) to the pumping of protons out of the inner
mitochondrial compartment.  It thus becomes energetically favorable
for protons to cross the membrane back into that inner compartment.
The channels that allow the protons back in are proteins that convert
ADP to ATP as the proton moves into the inner chamber.  UCP's provide
another pathway for the protons to move into that chamber, and that
other pathway is not coupled to the production of ATP.  Thus the
energy burned (and heat created) in pumping out some of those protons
is not converted into energy usable to the animal.  By modulating the
activity of UCP's, mammals can regulate the relative amount of energy
they expend to maintain their body temperature.  I suspect this is one
of the "as-yet-poorly understood metabolic pathways" to which Tom
referred.  So... if anybody needs a thesis project I say they should
start looking at the comparative biology of UCP homologs in a variety
of animals...

Mickey Rowe     (mrowe@indiana.edu)