A recent NASA-funded study has observed findings about the molecular processes that might have shaped the origins of life on Earth. Research published in Nature Communications suggests that ribonucleic acid (RNA), a molecule believed to have predated DNA, exhibits no inherent bias in producing the left- or right-handed versions of amino acids. This challenges long-standing assumptions about why life predominantly uses left-handed amino acids in its proteins, a phenomenon known as homochirality.
The Enigma of Molecular Handedness
Amino acids, the essential building blocks of proteins, exist in two mirror-image forms: left-handed and right-handed. Life on Earth exclusively relies on the left-handed variety, though there is no apparent reason right-handed amino acids would not function similarly. This phenomenon has baffled scientists, as it appears to reflect a fundamental aspect of biology. The current study, led by Irene Chen, Professor at the UCLA Samueli School of Engineering, tested ribozymes—RNA molecules capable of acting like enzymes under early-Earth conditions. The results indicated that ribozymes could favour either handedness, undermining the notion that RNA inherently favoured the left-handed type.
Implications for Life's Early Evolution
The research involved simulating primitive Earth conditions, where ribozymes were exposed to amino acid precursors. In 15 tested combinations, no consistent bias towards left-handed amino acids was observed. This discovery suggests that homochirality may have emerged through evolutionary processes rather than as a result of RNA's chemical preferences. Co-author Alberto Vázquez-Salazar, a UCLA postdoctoral scholar, noted that these findings imply that life's molecular handedness likely arose later in its development.
Future Research on Life's Molecular Origins
Jason Dworkin, Senior Scientist at NASA's Goddard Space Flight Center, emphasised that understanding life's molecular properties informs the search for extraterrestrial life. Current analysis of samples from asteroid Bennu, brought back by NASA's OSIRIS-REx mission, includes studying amino acid handedness. Such investigations may uncover further clues about the origin of homochirality and its role in life's development.
The research was funded by NASA, the Simons Foundation, and the National Science Foundation, contributing valuable insights into one of life's most profound mysteries.
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