How Life Was Constructed and Why It is Largely Right-Handed

July 1, 2020 – As a lifelong left-handed person I’m not sure if I should be offended by this interesting discovery about how life is based on right-handedness.

The basic molecular construct of our existence, the double-helix we call DNA, it turns out appears to spiral always to the right and not to the left. It doesn’t matter what type of life as we know it…always a right ascending spiral.

In chemistry, non-living molecules don’t discriminate. They mix both right and left-oriented constructs. But not the RNA and DNA, the molecules of life.

Why?

The article appearing in The Astrophysical Journal Letters entitled, “The Chiral Puzzle of Life” was published last month and talks about life having a “chiral bias.” That means the molecules display a specific orientation that cannot be replicated when looking at them in a mirror. The authors, Noemie Globus of New York University and the Center for Computational Astrophysics, and Roger Blandford of Stanford University, in their words, state that “living organisms comprise a system of molecules organized with specific handedness.”

In this case, it suggests a biological bias to right-hand dominance as determined by the RNA and DNA helixes. The helical structures of chained nucleotides rise up always spiraling to the right. This tendency ensures the stability of the genetic code and ensures few errors in replication. One could imagine if there were no chirality, that a percentage of DNA and RNA would display left-handed chirality, and the effect could become quite chaotic during replication.

What caused right-handed RNA and DNA?

The authors speculate that cosmic radiation played a key part. Subatomic particles like prions and muons delivered from the stars and cosmic background radiation may have bombarded long-chain molecules eventually leading to right-handedness becoming inherent to the beginning of life.

Muons, for example, contain enough energy to create a spin polarity when striking a molecule and the authors believe that this along with other potential particles within cosmic radiation became the instruments that led to stable helical structures ascending to the right.

That’s not to say that cosmic particles could equally have delivered left-handed spin producing very different constructs, but would they have led to a self-replication?

One can speculate that in the early Universe when stars and planets were first forming, left and right-handed chirality were equally on display producing all kinds of long-chain molecules of which some could have emerged as self-replicating.

To this day, we find evidence of amino acid molecules not just here on Earth that display left-handed chirality. Might this suggest that left-handedness chemistry constructs don’t lead to life?

The authors hypothesize how life emerged in the early Universe believing that its emergence had a lot to do with the building of long-chain molecules with stable architecture that allowed for rapid decoupling and recoupling of its sub-components, the nucleotides capable of grabbing the base sugars such as adenine, cytosine, guanine, and thymine which could be found nearby in the environment. The bombardment caused by cosmic particles influenced the molecules to spin to the right.

What would these early environments look like? Astrobiologists believe that good candidate environments include meteorites containing nucleotides, hydrothermal vents in the early oceans, volcanoes, and natural wet and dry cycles such as those brought on by tidal movements. All or one could have promoted the growth of long-chain molecules impacted by irradiation to display a polarity bias to right-handed chirality.

In any case, as we further explore the Solar System including asteroids, the Moon, and Mars, we may find biogenic evidence that supports universal right-handedness in life’s molecular origins. The authors of the paper described in this posting predict the likelihood that we will find just that, that all life in the Universe will display the same handedness which does nothing for me as a natural southpaw. But that’s life!