Friday, 14 May 2010

Chirality – it’s a Left-Handed Universe!

Meeting Apollo Astronaut Charles Duke - fellow left-hander!

I’m left-handed, so is my sister. Because of this, and also because left-handed people are generally in the minority, I’ve always tended to notice when someone else is left-handed. In a world largely designed for the benefit of right-handers, some things can be more difficult for me – scissors, can openers, writing without smudging, musical instruments – the list is long. As a consequence, left-handers are generally more skilled at using their non-dominant hand than their right-handed counterparts. I once met Apollo astronaut Charles Duke, and remarked on the fact he was left-handed and didn’t this make it more difficult to handle controls on the spacecraft? Apparently, not so, as the craft were designed not with the human occupants in mind but rather where everything would fit in the limited space of the environment.

Where is this leading? Well, today I came across the term ‘Chirality’, which comes from the Greek kheir which means ‘hand’. The easiest way to understand the concept is to hold your left hand up to a mirror. The image you will see will be that of a right hand – a mirror image of your left hand. This phenomenon occurs throughout nature, with some fascinating consequences. For example, when I was born in 1958 there was a popular sedative drug available for pregnant mothers. The drug was called thalidomide, and is now notorious for the dreadful birth defects suffered by many of the babies of that period. The problem with thalidomide was that it was chiral – it had both left- and right-handed properties, and was made up af a 50/50 mix. The left-handed molecule provided the sedative property, whilst the right-handed molecule (it was discovered) led to the abnormalities in foetus development. Fortunately for me, my mother declined the drug, although I did have childhood friends with missing fingers and worse because of it.

Aspartame, beloved of diabetics for its sweetening properties, has a right-handed molecule which tastes bitter! And, most interesting of all, all human proteins are built from left-handed amino acids. So, it seems that whatever hand you use to sign your name, we are all left-handed!

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