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Research conducted by Harvard University may have solved the puzzle of how life became molecularly right-handed. In the paper “Origin of biological homochirality by crystallization of an RNA precursor on a magnetic surface”, published in The progress of scienceresearchers explain how it all could have started with the right kind of rocks.
Molecules can be left-handed, right-handed, or both. RNA and the sugars that make up DNA are right-handed molecules. No one knows why or if there is a reason beyond chance that life began with the right hand.
By analogy, human hands can be right or left, and are mirror images of each other, meaning they cannot be superimposed without looking in the wrong direction. Molecules can have similar structural symmetry.
In much the same way that right-handed people have difficulty with left-handed scissors, or left-handed guitarists have to swap strings and play the instrument backwards, the molecules don’t interact the same way when they’re left- or right-handed. Once started, it makes sense that the building blocks of life continue with the same handedness.
One intriguing idea is that left-handed cosmic rays destroyed left-handed DNA precursors just as life began on Earth.
Ribo-amino oxazoline (RAO) is a crucial RNA precursor for two of the RNA nucleotides, cytosine and uracil. RAO also forms a crystal structure that can be right or left handed which, once the crystal begins to form, right or left handed, only bonds with other molecules of the same handedness.
By placing RAO on magnetite (Fe3OR4), researchers could achieve 100% handedness of RAO crystallization, left or right, depending on the spin exchange interaction and the degree of spin alignment (magnetization) on the active surface.
Earth’s most abundant naturally occurring magnetic mineral, magnetite, would have had many opportunities for interaction with RAO in early times. However, the researchers say the effect is unlikely to occur in contact with solution particles such as mud, but rather on sedimentary rock surfaces.
Even with current discoveries that could unlock two of the four nucleotide components of RNA, two more are still missing. So far, the origin story notes that common and naturally occurring components at room temperature can initiate the process. If the next two are found to have similar requirements, it would indicate that life on any Earth-like planet in the universe could just as easily have started.
S. Furkan Ozturk et al, Origin of biological homochirality by crystallization of an RNA precursor on a magnetic surface, The progress of science (2023). DOI: 10.1126/sciadv.adg8274
S. Furkan Ozturk et al, Chirality-induced magnetization of magnetite by an RNA precursor, arXiv (2023). DOI: 10.48550/arxiv.2304.09095
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