Re: genetic codes and digestion

On Mon, 14 Aug 2006 10:23:08 -0700, Ben Crowell <"crowell06 at
lightSPAMandISmatterEVIL.com"> wrote:

I'm currently working on a story, and a reader raised a
question about the science in it. The premise of the story
is that bugs (not insects) show up on earth that have
a previously unknown genetic code, not DNA or RNA. The reader
expressed skepticism that these bugs would be able to digest
Earth organisms as food. My assumption (I'm a physicist, not
a biochemist) would be that it would work like this: regardless
of your genetic code, the genes code for proteins, and you could
presumably make exactly the same proteins as normal earth
organisms.

Not necessarily. Proteins are assembled from amino acids, and
terrestrial life does not use all possible amino acids. We
evolved the genetic coding and enzymatic toolkit for a diverse
enough set of amino acids to do whatever we needed to do, and
didn't much bother with anything more than that.

Alien life, carbon/water alien life at least, would presumably
do something similar, but it wouldn't come up with the *same*
set of amino acids.

This may or may not be a problem. Some terrestrial organisms
are capable of internally synthesizing every amino acid they
need, from simple raw materials. Others, require that some
necessary amino acids be provided with their food. If your
alien critters fit the latter model, they probably won't get
what they need.

But a nigh-omnivorous "bug" that is equipped to break down
whatever it eats into the simplest biologically useful raw
materials and building from them its own brand of proteins
and whatnot, is quite plausible.


After all, every organic compound on Earth falls into one
of two categories - stuff simple and universal enough that
you can expect to find it anywhere there's a lukewarm mix
of carbon and water, and stuff that some organism figured
out how to make from the simple stuff.


These proteins would determine what you could digest. A
carbohydrate or a lipid is a pretty generic energy-storing
chemical, and the ability to digest it shouldn't be
sensitive to your genetic code. Have I got this right?

Simple carbohydrates and lipids are *probably* nigh-universal
to carbon/water biochemistries, though there's always room for
a surprise or ten.


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Relevant Pages

  • Origins of Life on Earth
    ... meteorite has shown that it is rich with amino acids. ... amino acids are found on Earth. ... other organic compounds by planetary infall. ... we can determine the age of the rock. ...
    (sci.bio.evolution)
  • Re: genetic codes and digestion
    ... a previously unknown genetic code, ... expressed skepticism that these bugs would be able to digest ... Earth organisms as food. ... of your genetic code, the genes code for proteins, and you could ...
    (rec.arts.sf.science)
  • Earths early haze
    ... Hazy skies on early Earth could have provided a substantial source of organic ... material useful for emerging life on the planet, according to a new study led ... would have provided a global source of food for living organisms," said ...
    (sci.bio.evolution)
  • Re: Genocidal SF
    ... believe that you can equate the inability to repel the invasion force ... with the lack of naval superiority. ... where Earth is from the Skinnies, and they never locate Sanctuary, ... carelessness on the part of the bugs. ...
    (rec.arts.sf.written)
  • Re: Some simple questions for the simplistic noncredible mind of DILV
    ... Why on earth do you persist on lying about Crick? ... Hoyle assumed that the 20 amino acids were present in the *soup* ... functioning proteins, the odds of the spontaneous generation of a cell is ...
    (uk.philosophy.atheism)