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September 12, 2005

Searching For Alien Life Here On Earth

Searching for right-handed amino acids:

So how can we be sure that the world about us isn't seething with alien bugs? I began researching this with Charles Lineweaver at the Australian National University. We identified several ways in which multiple genesis episodes might have left traces in Earth's geological or biological record. The real prize would be the identification of a truly alien microbe right under our noses. But how would we spot such a thing amid the welter of familiar life?

A possible answer was provided by my wife, a science journalist. To make proteins, organisms use amino acids, whose molecules resemble left-handed gloves. Look at them in a mirror and they would be right-handed. The right-handed forms are not hard to make, but life does not use them. The best explanation for this preponderance of left-handed amino acids is that it represents a frozen accident: early on in the genesis process, a random choice was made and life got stuck with it. But if there were a second genesis, then the odds are 50-50 that the opposite choice would be made. This "mirror life" might resemble "our" life in most important respects, but not in its handedness. And because left and right-handed life couldn't mix, mirror life would peacefully co-exist with our form of life...

Handedness, or "chirality," refers to the orientation of atoms around a central carbon atom. The carbon atom has four points of joining with other atoms, and two different carbon atoms can join with the same four other atoms and yet be chemically distinct. That's because of how they're oriented around the central carbon atom-- if you use four of your fingers of your left hand to represent the chemical bonds to other atoms, taking your palm to be the central carbon atom, you can see that you can stick on four different atoms (just call them red, blue, green, yellow) such that the this hand-atom won't superimpose itself over, or be identical to, a "Carbon molecule" represented by the same atoms connect to the same fingers your right hand.

That's what makes Splenda/sucralose, which is different from real sugar only in the chirality or arrangement of atoms around a central carbon atom, chemically distinct from real sugar or sucrose. The body can process one but can't do anything with the other except excrete it as metabolically useless.

The study of "wrong-handed" amino acids is technically known as "Bizarro biology." Scientists postulate that a being constructed entirely of right-handed amino acids would say things like "Me so happy, me want to cry" and would say "Hello" when he leaves and "Goodbye" when he first shows up.

He would also derive power from kryptonite, rather than being all pussified by it.

No thank you to cutaway. Cutaway a good tipper, me hate him so much.

Science Weenie Update: Dave Eaton, making trouble for me as usual, says that sucralose isn't different from sucrose only in its handedness. It also has a few oxygen atoms replaced by chlorine.

Me love corrections. When me get corrections, me so thankful me want to pound stupid-pointy-head into a soupy pulp.

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posted by Ace at 12:59 PM

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