Homochirality – the foundation of life
This is interesting as hell if you are a geek. If you’re too busy ranting about the election, sitting in front of a game console, or watching soaps, go ahead and skip this post. For those of you still with me, we’re talking about the subject of my first novel, PARADOX. We’re talking about chemicals, DNA, atoms, and the forces that make the world go round.
The image above is the molecule LIMONENE. A molecule is a compound of atoms, remember, which are the smallest units of a single element. A center has the neutrons and protons, and in shells around the nucleus zing the electrons. Molecules, like atoms, are three dimensional things. Think of them as Tinkertoys, it helps.
Water is a molecule, made of two hydrogen atoms and one oxygen atom. It is always the same no matter how it combines because the two hydrogen atoms always sit in the outermost shell of the oxygen atom. That will never change.
Most molecules are chiral. They can exist only if the atoms hook up together in the correct order at the correct electron. DNA is one of those molecules. You’ve all seen an illustration showing the twisting molecule, sometimes two meters long, all scrunched up into a microscopic package – it’s truly amazing. All biological DNA but for a few archaic bacteria twist to the right.
Huh? Th
e only way I can explain it is this: The strips of DNA in the foreground are spiraling down FROM the right in the picture. If you see a drawing of the strips in the foreground going left, it is drawn incorrectly. But that’s not what the post is about. What I want to explain is how it got like this and why it’s important. The geeky part is coming, hang in there.
IT MATTERS which way the thing goes, because if you take a look at the LIMONE molecule above, if it chirals to the left, (L or S) it smells and tastes like lemons. If it spirals to the right (R or D) it smells and tastes like oranges. The molecule cannot match up with it’s own mirror image in 3D. Your hands are like that. The palms can meet, but that is not because they are symmetric. If they were symmetric they would look the same from your viewpoint. Place one over the other in front of you (not palm to palm).They are not mirror images of each other.
Where am I going with this? Remember, salts, minerals, chemicals can and mostly are asymmetrical. All over the world with few exceptions (which I’ll theorize about shortly) amino acids spiral to the right and sugars spiral to the left. In a lab environment, we’ve created compounds that still spiral, but in both directions. Why in nature are these compounds homochiral, but heterochiral in the lab?
What mechanism drives the biological compounds to homochirality back in the prebiotic world? If you think back to our atoms and their electrons, could it be that a tiny (really tiny) bit of energy happened to pull the molecule a little one way or the other? It could have just as easily been to the left as to the right. This small imbalance in the two different enantiomers is real and in my humble opinion could have been the result of the direction of planetary motion. Earth revolves counterclockwise around the sun and its own axis. By considering the earlier Earth and its molten core, a bit of centrifugal motion may have been the magic ingredient to push biology one direction or another.
I’m at the really geeky part now. If this might be true, then it might be true that on Venus, which spins clockwise on its axis, lifeforms would have the opposite chirality. And here is something we don’t know. How long ago did Venus flip? Most likely, it was early on when the solar system was forming, and models suggest that it was hit by some planetessimal, possibly the fragment of which became Mercury. Another time for that avenue.
So, if Venus were not such a hot and hostile place, would we be able to eat vegetation that arose there or only if it formed before the planet was kicked over? Are the theoretical life forms on Venus opposite from Earthlings and does their DNA spiral left? Are there both biological creatures – those that developed before the collision and after? Wouldn’t it be a fantastic mission, to land on Venus, pick up some creatures, and find out which way they tick?
More fodder for my science fiction novels, Paradox is exactly this scenario. The planet around Beta Hydri suffered a collision with a space body and was turned upside down so that the sun rises in the west and sets in the east. And the first life forms to develop were similar to Earth – right enantiomer DNA until the planet changed, and then new life forms developed with left enantiomer DNA.
In the last 20 years or so, the classification of biological life forms has itself evolved, and now we have Daredevil Kooky Prince Charles On Friday Goes Surfing. Daredevil stands for DOMAIN, and further divides the kingdoms into Archaea, Bacteria, and Eukarya (this last one holds fungi, plants, and animal kingdoms). Should we find such life forms, on Mars or one of Jupiter’s moons how will we classify them? Do they get their own Domain or Kingdom, will they exhibit the D enantiomer or the L, and why? Finding life on another world is more than exciting, it’s an entirely new science to explore. A hundred years ago there was no job for the pizza delivery man. A hundred years from now, I guarantee we will have exobiologists answering these very questions.
Genetic engineering is arguably the most significant single tool humans possess to change their future. It affects everything you can think of. Eradicating viruses, eliminating bacterial resistance, stopping birth defects, cleaning up polluted water, increasing crop yields, all on the radar in the genomic future of humans. I’d like to elaborate on each of those, but suffice to say the essay would become a text book.
Genetic engineers have found a way to reduce the severity of mental retardation in children with an extra chromosome 21 (Down’s syndrome) if they are aware of the mutation and can intervene before 10 weeks when the neural pathways begin to develop. New technology allows doctors to use fragments of fetal DNA found in the mother’s blood to diagnose the condition so an amniocentesis or CVS doesn’t have to be performed (increasing chance of miscarriage), which by the way is performed too late to correct the issue. Although heart development and characteristic features are already set, the mental retardation that accompanies Down’s Syndrome can be significantly reduced offering these children a more traditional future of independence and community acceptance.