Archive for category Chemistry
Remember the arsenic-based bacteria that it turned out probably weren’t arsenic based at all? There’s echoes of that in today’s Daily Mail story: “Life on Earth DID begin in space, according to study of samples found on meteorites“.
“Life began in space” is a rather bold statement to make, and it doesn’t take long before the Mail back tracks:
A meteorite study has strengthened evidence that life on Earth began in space.
Many experts believe biological raw ingredients were carried to Earth in lumps of asteroid rock.
A key clue lies in the molecular structure of amino acids, the building blocks of proteins and living organisms.
The molecules come in two mirror-image varieties, known as left and right-handed. But only left-handed amino acids are found in nature.
To be fair to The Mail, the rest of the article isn’t too bad – unsurprising really, since it’s basically just a shortened version of the NASA press release. But that headline!
Left and right-handedness here refers to something called chirality – a chiral molecule is one which, no matter how much you rotate it, cannot be superposed on its mirror image. Amino acids (shown in the picture above) are almost all chiral*, which leads to something rather interesting. You see, your body builds proteins by linking together long chains of amino acids to form very delicately folded structures. Because left-handed and right-handed amino acids are different shapes, you can’t simply swap one for the other without messing up the entire chain. Similarly, your digestive enzymes are very precisely shaped so that they can “grab onto” left-handed amino acids but not right-handed ones. As far as your body’s concerned, right-handed amino acids are more or less invisible.
Where this gets fascinating, though, is that all life on Earth uses left-handed amino acids to build proteins. Why evolution “picked” left-handed amino acids over right-handed isn’t certain. It could just have been that in the beginning both left-handed and right-handed amino acids existed, racing to form life, and the left-handed ones won. Or it could have that something called circularly polarised radiation either from the Sun or from distant dying stars destroyed some of the right-handed acids as soon as they formed, giving the left-handed acid a headstart.
NASA’s discovery – that meteors contain slightly more of the left-handed form of a specific amino acid than the right-handed form – suggests that the latter is true. But that’s all it suggests. It’s a shame; this a very interesting story on its own, and written up by anyone other than our anonymous friend Daily Mail Reporter it could have been fascinating to read and could have got readers a tiny bit more interested in science.
Instead, the Mail just nicks the press release, sticks a blatantly misleading headline on it and pumps it onto the internet in hurry to beat all the other newspapers. After all, a page hit is a page hit, regardless of whether the readers get through the whole thing or just scan three lines before releasing they’ve been misled.
* The one exception is the smallest amino acid, glycine, which is too simple to have a mirror image.