A good friend and former colleague lent me a book a few weeks ago. The title of the book is “The Disappearing Spoon“.
It’s an excellent read, especially if you are a science nerd like I am.
The author, Sam Kean, tells wild, wacky, and intriguing stories about elements on the periodic table. Sound like a page-turner? It is.
Buried in a story about the contributions of the great French biologist Louis Pasteur is the chemical definition of life.
Apparently, according to chemistry, life is left-handed.
I have always been interested in “handedness” because I can’t easily tell left from right.
There have been many times when I am giving my husband driving directions and I tell him to “Turn left, no right, I mean left… Right.”
The quickest way for me to tell left from right is to look at the hand wearing my wedding ring. I know that’s my left hand.
Before I was married, I had to mimic pledging allegiance. I knew my right hand went over my heart.
The typical method of teaching children to tell left from right, identifying your left hand as the one that forms an “L” with your index finger and thumb, didn’t work for me. In addition to being unable to tell left from right, I often drew many of my letters backward as a child and could not immediately tell which hand was making the (forward) letter “L“.
Pledging allegiance was a more reliable method.
Teaching the concept of equilibrium was baffling for me (I was a chemistry teacher), because I constantly had to refer to the “left” and “right” side of chemical equations.
My students would snicker as they caught me sliding sideways glances to my wedding ring to tell which side of the equation was the “left“.
Kids can be so cruel.
Here is my explanation of why life is left-handed in three steps.
- The relatively large molecules that make up your body and all living things are made up of mostly carbon, hydrogen, and oxygen atoms.
These carbons, hydrogens, and oxygens are arranged in a certain very specific structure in each molecule. A small molecule containing three carbons, six hydrogens, and two oxygen atoms, for example, has 26 possible permutations, each one with completely different properties.
- Three-dimensional molecules may be arranged in a left-handed orientation or a right-handed orientation. The name for this is “chirality“.
Chiral molecules are mirror images of each other, just like your left and right hands.
Also just like your left and right hands, the left and right-handed molecules are decidedly not the same. The left-handed isomer of the chemical carvone smells like spearmint, which is not surprising. Most of the essential oil from spearmint is made up of carvone. The right-handed isomer of carvone smells like the caraway seeds that flavor rye bread.
- Life is left-handed.
You see, every protein that composes your body and the bodies of all living things from giraffes to amoebas to sunflowers, is made from molecules with a left-handed orientation. We are all left-handed at heart.
One of the worst epidemics of birth defects in the 20th century was caused by scientists not understanding chirality.
Pregnant women were given the drug thalidomide to prevent morning sickness. Only the left-handed form of the drug, however, was benign. The right-handed version of the molecule caused unborn babies’ limbs to develop improperly or not at all.
Living things naturally produce either the left-handed or right-handed version of molecules. Not both.
Producing the same substances in the lab (unless special catalysts are used) produces a mixture of both the left and right-handed versions.
The lab that produced thalidomide had no idea that when it produced a useful chemical to reduce the suffering of pregnant women, it was simultaneously producing a similar, but not identical chemical that caused horrendous birth defects in their unborn babies.
Chirality matters, as we found out the hard way.
We are all experiencing life with a left-handed twist.
(Left-handed. That’s the hand with the wedding ring.)
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