The Nobel Prize in Chemistry has been awarded to French scientist Henri B. Kagan and Japan's Kenso Soai for solving a chemical mystery that has puzzled scientists for over a century: why life exclusively uses one mirror-image version of certain molecules. The answer, it turns out, is chirality - a property where molecules come in left- and right-handed forms, like your hands. And no, this doesn't mean your left hand is plotting against your right.

Amino acids, the building blocks of proteins, exist as two mirror-image forms. But living organisms on Earth only function with one of those forms. The Nobel laureates figured out how nature selectively produces the correct version, a phenomenon known as homochirality. In the lab, chemical reactions typically create a 50-50 mix of both left- and right-handed molecules, which is a problem when making drugs because each version behaves differently in the body. One might fight disease while the other does nothing or even causes harm. So, you know, slightly important.

Speaking to the Nobel Prize press conference this morning over the phone, Kenso Soai said: "This is one of the most exciting days of my life." He probably would have said more, but he was busy being a Nobel laureate.

Heiner Linke, chair of the Nobel Committee for Chemistry, explained: "Henri Kagan and Kenso Soai have provided a solution to a chemical mystery that is over a century old: how homochirality - the selective production of the correct version of a molecule - can emerge spontaneously. The chemical reactions they have developed are spectacular."

Henri Kagan, who is at Université Paris-Sud, first discovered a new way of manipulating chemical reactions in 1986. This allowed him to create a greater excess of one of the mirror images than had previously been thought possible. Kenso Soai from Tokyo University of Science took the next step in 1995. He published a scientific paper in the journal Nature describing the first ever chemical reaction that had the potential to be homochiral - producing only the desired version of an organic molecule. In 2003, he finally succeeded in controlling a reaction in which only one of the two possible mirror images was formed. "Other than life itself," the Nobel Committee said in a statement, "no one had previously achieved this feat." Which is a fancy way of saying: nice job, you've caught up with nature after four billion years.

At the press conference on Wednesday, Kenso Soai praised the "many, many excellent researchers" in this field. Professor Robert Mokaya, president of the UK's Royal Society of Chemistry said it was a "powerful example of how fundamental chemistry can underpin solutions to some of the biggest challenges facing society." He added: "Different isomers (or versions of molecules) can have completely different biological and physical effects, so they are crucial in finding effective medicines to treat all sorts of illnesses." So next time you take a pill, thank chirality - or at least the Nobel laureates who figured out how to make the right version.

Prof Angus Davison, from the University of Nottingham, studies the biology of chirality and said that the Nobel-winning chemistry could help reveal how and why life favours "one-handedness". "In ways that we don't yet quite understand, the chirality of the basic building blocks of life ends up making bodies that are themselves also chiral," he told BBC News. This was the foundation, he explained, of our hearts being on left hand side of our bodies and snail shells that coil to the right. So if you're left-handed, blame chemistry.

Peter Somfai, a member of the Nobel Committee for Chemistry, said the research awarded this year's prize has become part of "our basic understanding of how chemistry functions". He said showing how a mirror image is created is "probably the most fundamental question in life - because somehow that happened four billion years ago when life was created. And now we have, for the first time, mimicked that in the lab". So congratulations to Kagan and Soai for winning the Nobel Prize and for finally giving life's asymmetry a proper explanation - and a well-deserved award.