One of the more fascinating bits of biochemistry is the odd "handedness" (technically called chirality) that a lot of biological molecules have. Chiral molecules come in a left-handed (sinistral) and a right-handed (dextral) form that are made of exactly the same parts but put together in such a way that they're mirror-images of each other, just like a left-handed and right-handed glove.
Where it gets really interesting is that although the left-handed and right-handed forms of biologically active molecules have nearly identical properties, they aren't equivalent in function. Nearly all naturally-occurring sugars are right-handed; amino acids, on the other hand, are all left-handed. No one knows why this is, but having evolved with this kind of specificity has the result that if you were fed a mirror-image diet -- left-handed glucose, for example, and proteins made of right-handed amino acids -- you wouldn't be able to tell anything apart by its smell or taste, but you would proceed to starve to death because your cells would not be able to metabolize molecules with the wrong chirality.
Molecular chirality was used to brilliant effect by the wonderful murder mystery author Dorothy Sayers in her novel The Documents in the Case. In the story, a man dies after eating a serving of mushrooms he'd picked. His friends and family are stunned; he'd been a wild mushroom enthusiast for decades, and the fatal mistake he apparently made -- including a deadly ivory funnel mushroom (Clitocybe dealbata) in with a pan full of other edible kinds -- was something he never would have done.
The toxic substance in ivory funnels, the alkaloid muscarine, is -- like many organic compounds -- chiral. Naturally-occurring muscarine is all left-handed. However, when it's synthesized in the lab, you end up with a mixture of right- and left-handed molecules, in about equal numbers. So when the contention is made that the victim hadn't mistakenly included a poisonous mushroom in with the edible ones, but had been deliberately poisoned by someone who'd added the chemical to his food, the investigators realize this is the key to solving the riddle of the man's death.
Chiral molecules have another odd property; if you shine a beam of polarized light through a crystal, right-handed ones rotate the polarization angle of the beam clockwise, and left-handed ones counterclockwise. So when an extract from the victim's digestive tract is analyzed, and a polarized light beam shined through it splits in two -- part of the beam rotated clockwise, the other part counterclockwise -- there's no doubt he was poisoned by synthetic muscarine, not by mistakenly eating a poisonous mushroom.
Turns out there may be a way to use this hand-in-glove property of biological molecules not to solve a murder, but to detect life on other planets. As with Dorothy Sayers's synthetic muscarine, organic compounds not produced by a living thing would almost certainly be a mixture of the two chiralities, right- and left-handed. Because organisms here on Earth are all so incredibly specific about which chirality they need (or create), it's a fair guess that living things on other worlds would have the same choosiness. And now a technique has been developed to detect molecular chirality in the light reflected from a forest from two kilometers away, by a spectropolarimeter on a helicopter flying at seventy kilometers per hour.
It only took seconds for the detector to tell the difference between light reflected from a living thing and light reflected from something inanimate, like a rock face or an asphalt road. Now that we're becoming increasingly good at seeing the faint light reflected from the surface of exoplanets, looking for rotation of the polarization angle of that light might be a quick way to see if there's anything alive down there."The next step we hope to take is to perform similar detections from the International Space Station (ISS), looking down at the Earth," said astrophysicist Brice-Olivier Demory of the University of Bern and MERMOZ (Monitoring planEtary suRfaces with Modern pOlarimetric characteriZation). "That will allow us to assess the detectability of planetary-scale biosignatures. This step will be decisive to enable the search for life in and beyond our Solar System using polarization."
One of the most devastating psychological diagnoses is schizophrenia. United by the common characteristic of "loss of touch with reality," this phrase belies how horrible the various kinds of schizophrenia are, both for the sufferers and their families. Immersed in a pseudo-reality where the voices, hallucinations, and perceptions created by their minds seem as vivid as the actual reality around them, schizophrenics live in a terrifying world where they literally can't tell their own imaginings from what they're really seeing and hearing.
The origins of schizophrenia are still poorly understood, and largely because of a lack of knowledge of its causes, treatment and prognosis are iffy at best. But much of what we know about this horrible disorder comes from families where it seems to be common -- where, apparently, there is a genetic predisposition for the psychosis that is schizophrenia's most frightening characteristic.
One of the first studies of this kind was of the Galvin family of Colorado, who had ten children born between 1945 and 1965 of whom six eventually were diagnosed as schizophrenic. This tragic situation is the subject of the riveting book Hidden Valley Road: Inside the Mind of an American Family, by Robert Kolker. Kolker looks at the study done by the National Institute of Health of the Galvin family, which provided the first insight into the genetic basis of schizophrenia, but along the way gives us a touching and compassionate view of a family devastated by this mysterious disease. It's brilliant reading, and leaves you with a greater understanding of the impact of psychiatric illness -- and hope for a future where this diagnosis has better options for treatment.
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