A recent groundbreaking NASA study has revealed a significant discovery about the protein configurations that may have given rise to early life, challenging existing scientific assumptions.
As NASA continues its exploration of the cosmos, unraveling the origins of life on Earth remains a top priority. By increasing our understanding of this mystery, scientists can gain essential clues and context for seeking life elsewhere.
The Essential Protein is Mysterious Components
Protein molecules are crucial building blocks of life as we know it. While only 20 different amino acids may make up all proteins, the diversity of potential arrangements means that proteins can be built for any task, from muscles to enzymes. Adding to the variety of amino acids, some exist in mirrored versions, referred to by biologists as “left-handed” and “right-handed.”
The mystery deepens when we consider the overwhelming preference for left-handed amino acids in lifeforms. While a lifeform built entirely of right-handed amino acids could theoretically thrive, this is not true in the real world. The two mirrored styles of amino acids rarely mix in nature, a phenomenon known as homochirality. The reason for this left-handed bias in life remains a tantalizing puzzle for biologists, fueling further research and exploration.
Examining the Blueprints for Clues
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the key players in the transformation of a primordial soup into a living organism. DNA serves as a detailed blueprint for constructing life forms from amino acids, a plan that RNA reads and executes. Given the complexity of this system and the gradual nature of evolution, scientists speculate that a much simpler system must have existed in the initial stages of the formation of early life on Earth. The ‘RNA World hypothesis’ is a leading theory in this regard, suggesting that the first life forms might have used RNA exclusively to construct and organize proteins into rudimentary forms.
If the RNA World theory is correct, biologists believe it may be a clue in solving the homochirality problem. Looking back to the beginning, something in the RNA may lead toward severe land-handed protein favoritism. Yet the study found no evidence of this preference, further confusing scientists about why right-handed molecules are so often rejected.
Early Life on Earth in a Lab
The NASA study examined ribozymes, RNA molecules responsible for building proteins, in a setting designed to mimic the conditions under which early life on Earth might have formed in a theoretical RNA World. Researchers recreated the primordial soup through a solution of ribozymes and amino acid precursors. The NASA biologists tested fifteen ribozyme combinations to understand how RNA would react to the precursors. While the recipe did yield the amino acid phenylalanine as expected, the results were still surprising.
At this most basic level of the building process, the study found that ribozymes could favor either mirrored amino option, not just one or the other. The heavy bias toward left-handed structures does not come from the RNA. This finding overturns the general expectation that early life forms likely had the same preponderance of left-handed amino acids as seen today.
Life in Outer Space
NASA continues to explore and seek any trace of extraterrestrial life but also seeks to discover if, in the reverse scenario, ancient meteorites and asteroids could have seeded amino acids on Earth. Unfortunately, biologists are missing key information about the first terrestrial life to make comparisons. Plate tectonics over extreme measures of time have erased the earliest fossil record, which would evidence the earliest life forms on Earth. This new experiment is one step closer to understanding the initial Earth life, potentially providing clues to both a cosmic origin and how to seek life elsewhere.
“Understanding the chemical properties of life helps us know what to look for in our search for life across the solar system,” said co-author Jason Dworkin, a senior NASA astrobiologist. “We are analyzing OSIRIS-REx samples for the chirality (handedness) of individual amino acids, and in the future, samples from Mars, will also be tested in laboratories for evidence of life including ribozymes and proteins.”
The paper “Prebiotic Chiral Transfer from Self-Aminoacylating Ribozymes May Favor Either Handedness” appeared on September 12, 2024 in Nature Communications.
Ryan Whalen covers science and technology for The Debrief. He holds a BA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.