Saturday, July 28, 2012

Saturday Omphaloskepsis: What if other life is right-handed?

Life on Earth is "left-handed". No, I don't mean that a majority of living things have hands, or even a preference for their left side. (Heck, some things don't even have a left side, since they are radially symmetrical.) No, in this case, I'm talking about the left-handed orientation of proteins (i.e., chirality).

On Earth, almost all proteins and sugars are left-handed: the proteins and sugars in our body, the proteins and sugars that we eat, the proteins and sugars that break down or interact with the proteins and sugars we consume or make are almost all left-handed (i.e., they display homochirality).

However, this doesn't preclude the presence of right-handed protein and sugars, or even the wide-spread presence of them.

What, then, would happen if we do discover extraterrestrial life that - instead of our left-handed homochirality - they are based on right-handed homochirality?

Would the proteins and sugars of these extraterrestrials be consumable by us? What about ours by them?

Would explorers find themselves surrounded by abundant proteins and sugars, but yet starve because their bodies can't process them?

Also, why hasn't this been addressed in science fiction, or do we just go with the assumption that either technology can fix the problem by reconstituting base elements into food or that life can only exist with the same (or effectively the same) basic mix of chilarity as on Earth?

All of this came to mind (again) when I saw this article at PhysOrg the other day:
Since life can't function with a mix of left- and right-handed amino acids, researchers want to know how life – at least, life on Earth -- got set up with the left-handed ones. "The handedness observed in biological molecules – left-handed amino acids and right-handed sugars – is a property important for molecular recognition processes and is thought to be a prerequisite for life," said Dworkin. All ordinary methods of synthetically creating amino acids result in equal mixtures of left- and right-handed amino acids. Therefore, how the nearly exclusive production of one hand of such molecules arose from what were presumably equal mixtures of left and right molecules in a prebiotic world has been an area of intensive research.
The story finishes with this additional twist that we will have to incorporate into our search for extraterrestrial life:
The result complicates the search for extraterrestrial life – like microbial life hypothesized to dwell beneath the surface of Mars, for example. "Since it appears a non-biological process can create a left-hand excess in some kinds of amino acids, we can't use such an excess alone as proof of biological activity," says Glavin.

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